[libclc] Enable -fdiscard-value-names build flag to reduce bitcode size

[wenju-he]

The flag reduces nvptx64--nvidiacl.bc size from 10.6MB to 5.2MB.

[frasercrmck]

LGTM, nice find.

I think this could optionally do with a comment before explaining what this flag is helping to achieve, but it's not a blocker.

[wenju-he]

I think this could optionally do with a comment before explaining what this flag is helping to achieve, but it's not a blocker.

it is explained at https://clang.llvm.org/docs/UsersManual.html#id72 and reducing size and verbosity is what this flag is intended for. I mean the flag doesn't have another meaning.

[llvm-ci]

LLVM Buildbot has detected a new failure on builder premerge-monolithic-linux running on premerge-linux-1 while building libclc at step 7 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/153/builds/38396

Here is the relevant piece of the build log for the reference

Step 7 (test-build-unified-tree-check-all) failure: test (failure)
...
PASS: lld :: COFF/exclude-symbols.s (98673 of 101648)
PASS: lld :: COFF/exclude-symbols-embedded.s (98674 of 101648)
PASS: lld :: COFF/arm64ec-import-range-ext.test (98675 of 101648)
PASS: cfi-standalone-lld-thinlto-x86_64 :: simple-fail.cpp (98676 of 101648)
PASS: lit :: discovery.py (98677 of 101648)
PASS: cfi-devirt-lld-thinlto-x86_64 :: cross-dso/icall/dlopen.cpp (98678 of 101648)
PASS: lld :: COFF/comdat-selection-associative-largest.s (98679 of 101648)
PASS: lld :: COFF/eh_frame_terminator.s (98680 of 101648)
PASS: lit :: googletest-timeout.py (98681 of 101648)
TIMEOUT: MLIR :: Examples/standalone/test.toy (98682 of 101648)
******************** TEST 'MLIR :: Examples/standalone/test.toy' FAILED ********************
Exit Code: 1
Timeout: Reached timeout of 60 seconds

Command Output (stdout):
--
# RUN: at line 1
"/etc/cmake/bin/cmake" "/build/buildbot/premerge-monolithic-linux/llvm-project/mlir/examples/standalone" -G "Ninja"  -DCMAKE_CXX_COMPILER=/usr/bin/clang++ -DCMAKE_C_COMPILER=/usr/bin/clang  -DLLVM_ENABLE_LIBCXX=OFF -DMLIR_DIR=/build/buildbot/premerge-monolithic-linux/build/lib/cmake/mlir  -DLLVM_USE_LINKER=lld  -DPython3_EXECUTABLE="/usr/bin/python3.10"
# executed command: /etc/cmake/bin/cmake /build/buildbot/premerge-monolithic-linux/llvm-project/mlir/examples/standalone -G Ninja -DCMAKE_CXX_COMPILER=/usr/bin/clang++ -DCMAKE_C_COMPILER=/usr/bin/clang -DLLVM_ENABLE_LIBCXX=OFF -DMLIR_DIR=/build/buildbot/premerge-monolithic-linux/build/lib/cmake/mlir -DLLVM_USE_LINKER=lld -DPython3_EXECUTABLE=/usr/bin/python3.10
# .---command stdout------------
# | -- The CXX compiler identification is Clang 16.0.6
# | -- The C compiler identification is Clang 16.0.6
# | -- Detecting CXX compiler ABI info
# | -- Detecting CXX compiler ABI info - done
# | -- Check for working CXX compiler: /usr/bin/clang++ - skipped
# | -- Detecting CXX compile features
# | -- Detecting CXX compile features - done
# | -- Detecting C compiler ABI info
# | -- Detecting C compiler ABI info - done
# | -- Check for working C compiler: /usr/bin/clang - skipped
# | -- Detecting C compile features
# | -- Detecting C compile features - done
# | -- Looking for histedit.h
# | -- Looking for histedit.h - found
# | -- Found LibEdit: /usr/include (found version "2.11") 
# | -- Found ZLIB: /usr/lib/x86_64-linux-gnu/libz.so (found version "1.2.11") 
# | -- Found LibXml2: /usr/lib/x86_64-linux-gnu/libxml2.so (found version "2.9.13") 
# | -- Using MLIRConfig.cmake in: /build/buildbot/premerge-monolithic-linux/build/lib/cmake/mlir
# | -- Using LLVMConfig.cmake in: /build/buildbot/premerge-monolithic-linux/build/lib/cmake/llvm
# | -- Linker detection: unknown
# | -- Performing Test LLVM_LIBSTDCXX_MIN
# | -- Performing Test LLVM_LIBSTDCXX_MIN - Success
# | -- Performing Test LLVM_LIBSTDCXX_SOFT_ERROR
# | -- Performing Test LLVM_LIBSTDCXX_SOFT_ERROR - Success
# | -- Performing Test CXX_SUPPORTS_CUSTOM_LINKER
# | -- Performing Test CXX_SUPPORTS_CUSTOM_LINKER - Success
# | -- Performing Test C_SUPPORTS_FPIC
# | -- Performing Test C_SUPPORTS_FPIC - Success
# | -- Performing Test CXX_SUPPORTS_FPIC