env-setup.sh: Remove GNU tools in the Docker image before building

This will help ensure that the GNU tools aren't hard coded anywhere as
the goal of the LLVM tools is to be as compatible as possible.

Closes: ClangBuiltLinux#122
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>

env-setup.sh

@@ -20,3 +20,32 @@ ccache --set-config=cache_dir=/travis/.ccache
 
 # Clear out the stats so we actually know the cache stats
 ccache -z
+
+# Ensure that GNU tools are not available when using LLVM tools
+function remove() {
+    mapfile -t files < <(type -ap "${@}")
+    for file in "${files[@]}"; do rm -vf "${file}"; done
+}
+
+case ${ARCH:=arm64} in
+    arm32*) CROSS_COMPILE=arm-linux-gnueabi- ;;
+    arm64) CROSS_COMPILE=aarch64-linux-gnu- ;;
+    ppc32) CROSS_COMPILE=powerpc-linux-gnu- ;;
+    ppc64le) CROSS_COMPILE=powerpc64le-linux-gnu- ;;
+esac
+
+# Remove the target's tools
+remove "${CROSS_COMPILE:-}"ar
+remove "${CROSS_COMPILE:-}"gcc
+[[ ${LD:-} =~ ld.lld ]] && remove ${CROSS_COMPILE:-}{ld,ld.bfd,ld.gold}
+
+# Remove the host tools if we are cross compiling
+if [[ -n ${CROSS_COMPILE:-} ]]; then
+    remove ar
+    remove gcc
+    [[ ${LD:-} =~ ld.lld ]] && remove {ld,ld.bfd,ld.gold}
+fi
+
+# Ensure that we always exit cleanly because a bash script's
+# exit code is always the code of the last command
+exit 0