Refine build instructions. Configure C/C++ compilers and linker via e…

…nvironment variables.

Signed-off-by: Vladimir Shiryaev <w@tagolog.com>

build_tools/build_mlir.sh

@@ -17,20 +17,28 @@ LLVM_INSTALL_DIR=$P4MLIR_REPO_DIR/install
 mkdir -p "$LLVM_BUILD_DIR"
 cd "$LLVM_BUILD_DIR"
 
+# Configure CMake flags
 # Note that P4C uses both RTTI and C++ exceptions, so we need to build LLVM/MLIR having them enabled as well
-cmake -G Ninja "$LLVM_REPO_DIR"/llvm \
-   -DCMAKE_INSTALL_PREFIX="$LLVM_INSTALL_DIR" \
-   -DLLVM_ENABLE_PROJECTS=mlir \
-   -DLLVM_BUILD_EXAMPLES=OFF \
-   -DLLVM_TARGETS_TO_BUILD="Native" \
-   -DCMAKE_BUILD_TYPE=Release \
-   -DLLVM_ENABLE_ASSERTIONS=ON \
-   -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ -DLLVM_ENABLE_LLD=ON \
-   -DLLVM_CCACHE_BUILD=ON \
-   -DLLVM_INSTALL_UTILS=ON \
-   -DLLVM_INCLUDE_BENCHMARKS=OFF \
-   -DLLVM_ENABLE_RTTI=ON \
-   -DLLVM_ENABLE_EH=ON
+CMAKE_FLAGS="-DCMAKE_INSTALL_PREFIX=\"$LLVM_INSTALL_DIR\""
+CMAKE_FLAGS+=" -DLLVM_ENABLE_PROJECTS=mlir"
+CMAKE_FLAGS+=" -DLLVM_BUILD_EXAMPLES=OFF"
+CMAKE_FLAGS+=" -DLLVM_TARGETS_TO_BUILD="Native""
+CMAKE_FLAGS+=" -DCMAKE_BUILD_TYPE=Release"
+CMAKE_FLAGS+=" -DLLVM_ENABLE_ASSERTIONS=ON"
+CMAKE_FLAGS+=" -DCMAKE_C_COMPILER=${CMAKE_C_COMPILER:-clang}"
+CMAKE_FLAGS+=" -DCMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER:-clang++}"
+if [[ -n "${LLVM_USE_LINKER}" ]]; then
+    CMAKE_FLAGS+=" -DLLVM_USE_LINKER=${LLVM_USE_LINKER}"
+else
+    CMAKE_FLAGS+=" -DLLVM_ENABLE_LLD=ON"
+fi
+CMAKE_FLAGS+=" -DLLVM_CCACHE_BUILD=ON"
+CMAKE_FLAGS+=" -DLLVM_INSTALL_UTILS=ON"
+CMAKE_FLAGS+=" -DLLVM_INCLUDE_BENCHMARKS=OFF"
+CMAKE_FLAGS+=" -DLLVM_ENABLE_RTTI=ON"
+CMAKE_FLAGS+=" -DLLVM_ENABLE_EH=ON"
+
+cmake -G Ninja "$LLVM_REPO_DIR"/llvm $CMAKE_FLAGS
 
 ninja
 ninja check-mlir

build_tools/build_p4c_with_p4mlir_ext.sh

@@ -28,8 +28,8 @@ if [ ! -d "$P4C_P4MLIR_EXT_DIR" ]; then
 fi
 
 # Configure CMake flags
-CMAKE_FLAGS="-DCMAKE_C_COMPILER=clang"
-CMAKE_FLAGS+=" -DCMAKE_CXX_COMPILER=clang++"
+CMAKE_FLAGS="-DCMAKE_C_COMPILER=${CMAKE_C_COMPILER:-clang}"
+CMAKE_FLAGS+=" -DCMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER:-clang++}"
 
 # Configure P4C CMake flags
 # https://github.com/p4lang/p4c/blob/main/CMakeLists.txt