[llvm] [ADT] Teach StringRef to derive from std::string_view (PR #113752)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `openmp-offload-amdgpu-runtime` running on `omp-vega20-0` while building `llvm` at step 5 "compile-openmp".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/30/builds/8952

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 5 (compile-openmp) failure: build (failure)
...
2.538 [4230/32/43] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/ELFAttributes.cpp.o
2.868 [4229/32/44] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/CachePruning.cpp.o
3.035 [4228/32/45] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/Caching.cpp.o
3.045 [4227/32/46] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/CodeGenCoverage.cpp.o
3.111 [4226/32/47] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/FloatingPointMode.cpp.o
3.112 [4225/32/48] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/FormattedStream.cpp.o
3.119 [4224/32/49] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/MathExtras.cpp.o
3.127 [4223/32/50] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/MemAlloc.cpp.o
3.154 [4222/32/51] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/DAGDeltaAlgorithm.cpp.o
3.169 [4221/32/52] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/CommandLine.cpp.o
FAILED: lib/Support/CMakeFiles/LLVMSupport.dir/CommandLine.cpp.o 
ccache /usr/bin/c++ -DGTEST_HAS_RTTI=0 -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.build/lib/Support -I/home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/lib/Support -I/home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.build/include -I/home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -fno-lifetime-dse -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-uninitialized -Wno-nonnull -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wno-misleading-indentation -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG -UNDEBUG -std=c++17  -fno-exceptions -funwind-tables -fno-rtti -MD -MT lib/Support/CMakeFiles/LLVMSupport.dir/CommandLine.cpp.o -MF lib/Support/CMakeFiles/LLVMSupport.dir/CommandLine.cpp.o.d -o lib/Support/CMakeFiles/LLVMSupport.dir/CommandLine.cpp.o -c /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/lib/Support/CommandLine.cpp
/home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/lib/Support/CommandLine.cpp: In function ‘void ExpandBasePaths(llvm::StringRef, llvm::StringSaver&, const char*&)’:
/home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/lib/Support/CommandLine.cpp:1127:60: error: call of overloaded ‘StringRef(const llvm::StringLiteral&)’ is ambiguous
 1127 |   for (StringRef::size_type TokenPos = ArgString.find(Token);
      |                                                            ^
In file included from /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/include/llvm/ADT/StringMapEntry.h:19,
                 from /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/include/llvm/ADT/StringMap.h:17,
                 from /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/include/llvm/Support/CommandLine.h:26,
                 from /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/lib/Support/CommandLine.cpp:18:
/home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/include/llvm/ADT/StringRef.h:103:28: note: candidate: ‘constexpr llvm::StringRef::StringRef(std::string_view)’
  103 |     /*implicit*/ constexpr StringRef(std::string_view Str) : Base(Str) {}
      |                            ^~~~~~~~~
/home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/include/llvm/ADT/StringRef.h:51:26: note: candidate: ‘constexpr llvm::StringRef::StringRef(const llvm::StringRef&)’
   51 |   class LLVM_GSL_POINTER StringRef : public std::string_view {
      |                          ^~~~~~~~~
/home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/include/llvm/ADT/StringRef.h:313:41: note:   initializing argument 1 of ‘size_t llvm::StringRef::find(llvm::StringRef, size_t) const’
  313 |     [[nodiscard]] size_t find(StringRef Str, size_t From = 0) const;
      |                               ~~~~~~~~~~^~~
/home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/lib/Support/CommandLine.cpp:1129:49: error: call of overloaded ‘StringRef(const llvm::StringLiteral&)’ is ambiguous
 1129 |        TokenPos = ArgString.find(Token, StartPos)) {
      |                                                 ^
In file included from /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/include/llvm/ADT/StringMapEntry.h:19,
                 from /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/include/llvm/ADT/StringMap.h:17,
                 from /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/include/llvm/Support/CommandLine.h:26,
                 from /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/lib/Support/CommandLine.cpp:18:
/home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/include/llvm/ADT/StringRef.h:103:28: note: candidate: ‘constexpr llvm::StringRef::StringRef(std::string_view)’
  103 |     /*implicit*/ constexpr StringRef(std::string_view Str) : Base(Str) {}
      |                            ^~~~~~~~~
/home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/include/llvm/ADT/StringRef.h:51:26: note: candidate: ‘constexpr llvm::StringRef::StringRef(const llvm::StringRef&)’
   51 |   class LLVM_GSL_POINTER StringRef : public std::string_view {
      |                          ^~~~~~~~~
/home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/llvm/include/llvm/ADT/StringRef.h:313:41: note:   initializing argument 1 of ‘size_t llvm::StringRef::find(llvm::StringRef, size_t) const’
  313 |     [[nodiscard]] size_t find(StringRef Str, size_t From = 0) const;
      |                               ~~~~~~~~~~^~~
3.240 [4221/31/53] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/ExponentialBackoff.cpp.o
3.310 [4221/30/54] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/ErrorHandling.cpp.o
3.321 [4221/29/55] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/DebugCounter.cpp.o
3.355 [4221/28/56] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/FoldingSet.cpp.o

```

</details>

https://github.com/llvm/llvm-project/pull/113752