[llvm] [llvm-dlltool] Implement the --identify option (PR #127465)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `flang-aarch64-sharedlibs` running on `linaro-flang-aarch64-sharedlibs` while building `llvm` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/80/builds/10351

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

```
Step 5 (build-unified-tree) failure: build (failure)
...
412.903 [5447/1/2118] Linking CXX shared library lib/libLLVMIRReader.so.21.0git
412.917 [5446/1/2119] Creating library symlink lib/libLLVMIRReader.so
413.336 [5445/1/2120] Linking CXX shared library lib/libLLVMObject.so.21.0git
413.356 [5444/1/2121] Creating library symlink lib/libLLVMObject.so
413.551 [5443/1/2122] Linking CXX shared library lib/libLLVMInterfaceStub.so.21.0git
413.563 [5442/1/2123] Creating library symlink lib/libLLVMInterfaceStub.so
413.841 [5441/1/2124] Linking CXX shared library lib/libLLVMObjCopy.so.21.0git
413.851 [5440/1/2125] Creating library symlink lib/libLLVMObjCopy.so
413.885 [5430/10/2126] Creating library symlink lib/libLLVMAArch64Desc.so
414.091 [5430/9/2127] Linking CXX shared library lib/libLLVMDlltoolDriver.so.21.0git
FAILED: lib/libLLVMDlltoolDriver.so.21.0git 
: && /usr/local/bin/c++ -fPIC -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wc++98-compat-extra-semi -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG  -Wl,-z,defs -Wl,-z,nodelete   -Wl,-rpath-link,/home/tcwg-buildbot/worker/flang-aarch64-sharedlibs/build/./lib  -Wl,--gc-sections -shared -Wl,-soname,libLLVMDlltoolDriver.so.21.0git -o lib/libLLVMDlltoolDriver.so.21.0git lib/ToolDrivers/llvm-dlltool/CMakeFiles/LLVMDlltoolDriver.dir/DlltoolDriver.cpp.o  -Wl,-rpath,"\$ORIGIN/../lib:/home/tcwg-buildbot/worker/flang-aarch64-sharedlibs/build/lib:"  lib/libLLVMObject.so.21.0git  lib/libLLVMOption.so.21.0git  lib/libLLVMTargetParser.so.21.0git  lib/libLLVMSupport.so.21.0git  -Wl,-rpath-link,/home/tcwg-buildbot/worker/flang-aarch64-sharedlibs/build/lib && :
/usr/bin/ld: lib/ToolDrivers/llvm-dlltool/CMakeFiles/LLVMDlltoolDriver.dir/DlltoolDriver.cpp.o: in function `llvm::dlltoolDriverMain(llvm::ArrayRef<char const*>)':
DlltoolDriver.cpp:(.text._ZN4llvm17dlltoolDriverMainENS_8ArrayRefIPKcEE+0x618): undefined reference to `llvm::identify_magic(llvm::StringRef)'
/usr/bin/ld: DlltoolDriver.cpp:(.text._ZN4llvm17dlltoolDriverMainENS_8ArrayRefIPKcEE+0xd40): undefined reference to `llvm::identify_magic(llvm::StringRef)'
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
414.097 [5430/8/2128] Linking CXX shared library lib/libLLVMLibDriver.so.21.0git
414.104 [5430/7/2129] Linking CXX executable bin/reduce-chunk-list
414.106 [5430/6/2130] Linking CXX shared library lib/libLLVMXRay.so.21.0git
414.150 [5430/5/2131] Linking CXX shared library lib/libLLVMDebugInfoDWARF.so.21.0git
414.156 [5430/4/2132] Linking CXX shared library lib/libLLVMRuntimeDyld.so.21.0git
414.192 [5430/3/2133] Linking CXX shared library lib/libLLVMDebugInfoPDB.so.21.0git
414.194 [5430/2/2134] Linking CXX shared library lib/libLLVMJITLink.so.21.0git
414.341 [5430/1/2135] Linking CXX shared library lib/libLLVMObjectYAML.so.21.0git
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/127465