build.sh: On Linux force use of latest Clang

CMake will default to GCC if it's available.
Force use of the latest Clang instead.
This can be overridden with CC, CXX, and CXXFLAGS

Fixed: google#8515

Author: dneto0

build.sh

@@ -224,6 +224,17 @@ BUILD_CUSTOM_TARGETS=
 UNAME=$(uname)
 LC_UNAME=$(echo "${UNAME}" | tr '[:upper:]' '[:lower:]')
 
+if [[ "$LC_UNAME" == "linux" ]]; then
+    # On Linux both GCC and Clang are commonly available, but CMake
+    # will default to GCC.
+    # Force use of Clang, and pick the highest-numbered version.
+    CLANG_VER=$(ls -1 /usr/include/clang | fgrep -v . | sort -n | tail -1)
+    export CC=${CC-/usr/bin/clang-$CLANG_VER}
+    export CXX=${CXX-/usr/bin/clang++-$CLANG_VER}
+    export CXXFLAGS=${CXXFLAGS--stdlib=libc++}
+    export COMPILER_OPTION="-DCMAKE_C_COMPILER=$CC -DCMAKE_CXX_COMPILER=$CXX -DCMAKE_CXX_FLAGS=$CXXFLAGS"
+fi
+
 # Functions
 
 function build_clean {
@@ -268,6 +279,7 @@ function build_desktop_target {
             -DIMPORT_EXECUTABLES_DIR=out \
             -DCMAKE_BUILD_TYPE="$1" \
             -DCMAKE_INSTALL_PREFIX="../${lc_target}/filament" \
+            ${COMPILER_OPTION} \
             ${EGL_ON_LINUX_OPTION} \
             ${FGVIEWER_OPTION} \
             ${WEBGPU_OPTION} \