[clang] [llvm] [cmake] Add config for riscv(32|64)-unknown-elf (PR #176353)

[Sam Elliott via cfe-commits]

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@@ -242,7 +242,8 @@ elseif(FUCHSIA OR UNIX OR CYGWIN)
   else()
     set(LLVM_HAVE_LINK_VERSION_SCRIPT 1)
   endif()
-elseif(CMAKE_SYSTEM_NAME STREQUAL "Generic")
+elseif(CMAKE_SYSTEM_NAME STREQUAL "Generic" OR
+       CMAKE_SYSTEM_NAME STREQUAL "Generic-ELF")
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lenary wrote:

What's the justification for not using `"Generic"` for RISC-V? Fuchsia seems to use "Generic" for their baremetal RISC-V builds (see line around 391 in `Fuchsia-stage2.cmake`)

https://github.com/llvm/llvm-project/pull/176353