[libc][Github] Perform baremetal libc builds

Currently there are no 32 bit presubmit builds for libc. This PR
performs 32 bit build only (no test) to check any changes that land in
libc break 32 bit builds.

Author: Prabhuk

.github/workflows/libc-fullbuild-tests.yml

@@ -24,30 +24,42 @@ jobs:
             cpp_compiler: clang++-22
             target: x86_64-unknown-linux-llvm
             include_scudo: ON
+            enable_baremetal_build: OFF
           - os: ubuntu-24.04
             build_type: Release
             c_compiler: clang-22
             cpp_compiler: clang++-22
             target: x86_64-unknown-linux-llvm
             include_scudo: ON
+            enable_baremetal_build: OFF
           - os: ubuntu-24.04
             build_type: MinSizeRel
             c_compiler: clang-22
             cpp_compiler: clang++-22
             target: x86_64-unknown-linux-llvm
             include_scudo: ON
+            enable_baremetal_build: OFF
           - os: ubuntu-24.04-arm
             build_type: Debug
             c_compiler: clang-22
             cpp_compiler: clang++-22
             target: aarch64-unknown-linux-llvm
             include_scudo: ON
+            enable_baremetal_build: OFF
           - os: ubuntu-24.04
             build_type: Debug
             c_compiler: clang-22
             cpp_compiler: clang++-22
             target: x86_64-unknown-uefi-llvm
             include_scudo: OFF
+            enable_baremetal_build: OFF
+          - os: ubuntu-24.04
+            build__type: Release
+            c_compiler: clang-22
+            cpp_compiler: clang++-22
+            target: armv6m-none-eabi
+            include_scudo: OFF
+            enable_baremetal_build: ON
           # TODO: add back gcc build when it is fixed
           # - c_compiler: gcc
           #   cpp_compiler: g++
@@ -102,6 +114,18 @@ jobs:
             -DCOMPILER_RT_SCUDO_STANDALONE_BUILD_SHARED=OFF"
         fi
 
+        if [[ ${{ matrix.enable_baremetal_build}} == "ON" ]]; then
+            export RUNTIMES="$RUNTIMES;libc"
+            export CMAKE_FLAGS="
+              -DCMAKE_BUILD_TYPE=Release
+              -DLLVM_LIBC_FULL_BUILD=ON
+              -DCMAKE_C_COMPILER_TARGET=armv6m-none-abi
+              -DCMAKE_CXX_COMPILER_TARGET=armv6m-none-abi
+              -DCMAKE_ASM_COMPILER_TARGET=armv6m-none-abi
+              -DCMAKE_C_FLAGS=-mfloat-abi=soft
+              -DCMAKE_CXX_FLAGS=-mfloat-abi=soft"
+        fi
+
         cmake -B ${{ steps.strings.outputs.build-output-dir }} \
         -DCMAKE_CXX_COMPILER=${{ matrix.cpp_compiler }} \
         -DCMAKE_C_COMPILER=${{ matrix.c_compiler }} \