[llvm-bugs] [Bug 49294] New: error: unknown argument: '-m32 -DLIBCXX_BUILDING_LIBCXXABI' when building 32-bit libc++ on x86_64/Linux

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=49294

            Bug ID: 49294
           Summary: error: unknown argument: '-m32
                    -DLIBCXX_BUILDING_LIBCXXABI' when building 32-bit
                    libc++ on x86_64/Linux
           Product: libc++
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: All Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: manojgupta at google.com
                CC: llvm-bugs at lists.llvm.org, mclow.lists at gmail.com

I am seeing a bunch of error: unknown argument: '-m32
-DLIBCXX_BUILDING_LIBCXXABI' when building 32-bit libc++ on x86_64/Linux.

Repro steps:

1. Build clang and compiler-rt builtins

$ cd /path/to/llvm-project
$ mkdir ../build && cd ../build
$ cmake ../llvm-project/llvm 
-DLLVM_ENABLE_PROJECTS="llvm;clang;lld;compiler-rt"
$ ninja clang builtins
$ 

2. Try to build 32-bit libc++ as standalone library
(We are in llvm-project/../build directory)

$ mkdir libcxx_build && cd libcxx_build
$  cmake -GNinja  ../../llvm-project/libcxx "-DLLVM_USE_LINKER=lld"
-DCMAKE_C_COMPILER=/path/to/build/bin/clang    
-DCMAKE_CXX_COMPILER=/path/to/build/bin/clang++     -DCMAKE_BUILD_TYPE=Release
"-DLIBCXX_USE_COMPILER_RT=ON" "-DLIBCXX_BUILD_32_BITS=ON"
"-DLIBCXX_CXX_ABI=libcxxabi"
"-DLIBCXX_CXX_ABI_INCLUDE_PATHS=../../llvm-project/libcxxabi/include"

I see following messages in the logs that look surprising. Seems like somewhere
"-m32" and "-DLIBCXX_BUILDING_LIBCXXABI" were combined as a single compiler
option which is causing clang to reject the option.

clang-12: error: unknown argument: '-m32 -DLIBCXX_BUILDING_LIBCXXABI'
-- Failed to find compiler-rt library
clang-12: error: unknown argument: '-m32 -DLIBCXX_BUILDING_LIBCXXABI'
-- Failed to find compiler-rt library
clang-12: error: unknown argument: '-m32 -DLIBCXX_BUILDING_LIBCXXABI'
-- Failed to find compiler-rt library

This does not cause any build breakage but I believe there is some incorrect
compiler flag handling somewhere.

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