support using an existing clang installation

add an option --host-clang which will skip building llvm,
and instead provide symlinks and wrappers for clang and
llvm tools.

Currently the clang version is detected, but it does not
affect the llvm version that will be downloaded and used.

build-all.sh

@@ -16,6 +16,7 @@
 
 set -e
 
+HOST_CLANG=
 LLVM_ARGS=""
 MINGW_ARGS=""
 CFGUARD_ARGS="--enable-cfguard"
@@ -26,6 +27,11 @@ while [ $# -gt 0 ]; do
     --enable-asserts)
         LLVM_ARGS="$LLVM_ARGS $1"
         ;;
+    --host-clang|--host-clang=*)
+        HOST_CLANG=${1#--host-clang}
+        HOST_CLANG=${HOST_CLANG#=}
+        HOST_CLANG=${HOST_CLANG:-clang}
+        ;;
     --full-llvm)
         LLVM_ARGS="$LLVM_ARGS $1"
         FULL_LLVM=1
@@ -78,11 +84,11 @@ while [ $# -gt 0 ]; do
     shift
 done
 if [ -z "$PREFIX" ]; then
-    echo "$0 [--enable-asserts] [--disable-dylib] [--full-llvm] [--with-python] [--disable-lldb] [--disable-lldb-mi] [--disable-clang-tools-extra] [--host=triple] [--with-default-win32-winnt=0x601] [--with-default-msvcrt=ucrt] [--enable-cfguard|--disable-cfguard] [--no-runtimes] [--no-tools] [--wipe-runtimes] dest"
+    echo "$0 [--host-clang[=clang]] [--enable-asserts] [--disable-dylib] [--full-llvm] [--with-python] [--disable-lldb] [--disable-lldb-mi] [--disable-clang-tools-extra] [--host=triple] [--with-default-win32-winnt=0x601] [--with-default-msvcrt=ucrt] [--enable-cfguard|--disable-cfguard] [--no-runtimes] [--no-tools] [--wipe-runtimes] dest"
     exit 1
 fi
 
-for dep in git cmake; do
+for dep in git cmake ${HOST_CLANG}; do
     if ! command -v $dep >/dev/null; then
         echo "$dep not installed. Please install it and retry" 1>&2
         exit 1
@@ -90,14 +96,16 @@ for dep in git cmake; do
 done
 
 if [ -z "$NO_TOOLS" ]; then
-    ./build-llvm.sh $PREFIX $LLVM_ARGS $HOST_ARGS
-    if [ -z "$NO_LLDB" ] && [ -z "$NO_LLDB_MI" ]; then
-        ./build-lldb-mi.sh $PREFIX $HOST_ARGS
+    if [ -z "${HOST_CLANG}" ]; then
+        ./build-llvm.sh $PREFIX $LLVM_ARGS $HOST_ARGS
+        if [ -z "$NO_LLDB" ] && [ -z "$NO_LLDB_MI" ]; then
+            ./build-lldb-mi.sh $PREFIX $HOST_ARGS
+        fi
+        if [ -z "$FULL_LLVM" ]; then
+            ./strip-llvm.sh $PREFIX $HOST_ARGS
+        fi
     fi
-    if [ -z "$FULL_LLVM" ]; then
-        ./strip-llvm.sh $PREFIX $HOST_ARGS
-    fi
-    ./install-wrappers.sh $PREFIX $HOST_ARGS
+    ./install-wrappers.sh $PREFIX $HOST_ARGS ${HOST_CLANG:+--host-clang=$HOST_CLANG}
     ./build-mingw-w64-tools.sh $PREFIX $HOST_ARGS
 fi
 if [ -n "$NO_RUNTIMES" ]; then

build-compiler-rt.sh

@@ -81,6 +81,8 @@ else
 fi
 
 cd llvm-project/compiler-rt
+# Use a staging directory in case parts of the resource dir are immutable
+WORKDIR=$(mktemp -d); trap "rm -rf $WORKDIR" 0
 
 for arch in $ARCHS; do
     if [ -n "$SANITIZERS" ]; then
@@ -123,10 +125,16 @@ for arch in $ARCHS; do
         -DCMAKE_CXX_FLAGS_INIT="$CFGUARD_CFLAGS" \
         $SRC_DIR
     cmake --build . ${CORES:+-j${CORES}}
-    cmake --install .
+    cmake --install . --prefix "${WORKDIR}/install"
     mkdir -p "$PREFIX/$arch-w64-mingw32/bin"
     if [ -n "$SANITIZERS" ]; then
-        mv "$CLANG_RESOURCE_DIR/lib/windows/"*.dll "$PREFIX/$arch-w64-mingw32/bin"
+        mv "${WORKDIR}/install/lib/windows/"*.dll "$PREFIX/$arch-w64-mingw32/bin"
     fi
     cd ..
 done
+
+if [ -h "$CLANG_RESOURCE_DIR/include" ]; then
+    # symlink to system headers - skip copy
+    rm -rf ${WORKDIR}/install/include
+fi
+cp -r ${WORKDIR}/install/. $CLANG_RESOURCE_DIR

install-wrappers.sh

@@ -17,9 +17,15 @@
 set -e
 
 unset HOST
+unset HOST_CLANG
 
 while [ $# -gt 0 ]; do
     case "$1" in
+    --host-clang|--host-clang=*)
+        HOST_CLANG=${1#--host-clang}
+        HOST_CLANG=${HOST_CLANG#=}
+        HOST_CLANG=${HOST_CLANG:-clang}
+        ;;
     --host=*)
         HOST="${1#*=}"
         ;;
@@ -30,7 +36,7 @@ while [ $# -gt 0 ]; do
     shift
 done
 if [ -z "$PREFIX" ]; then
-    echo $0 [--host=triple] dest
+    echo $0 [--host=triple] [--host-clang[=clang]] dest
     exit 1
 fi
 mkdir -p "$PREFIX"
@@ -58,6 +64,44 @@ else
     esac
 fi
 
+if [ -n "${HOST_CLANG}" ]; then
+    HOST_CLANG_EXE=$(command -v $HOST_CLANG)
+    HOST_CLANG_VER=$(echo "__clang_major__ __clang_minor__ __clang_patchlevel__" | $HOST_CLANG_EXE -E -P -x c - | xargs printf '%d.%d.%d')
+
+    mkdir -p $PREFIX/bin
+
+    # ex. /usr/lib/llvm-17/lib/clang/17
+    resdir=$($HOST_CLANG -print-resource-dir)
+    # ex. /usr/lib/llvm-17
+    llvmdir=${resdir%/lib/clang/*}
+    # ex /lib/clang/17
+    clangres=${resdir#$llvmdir}
+
+    mkdir -p $PREFIX$clangres
+
+    # link the header directory, prevent modification
+    ln -snf $resdir/include $PREFIX$clangres/include
+
+    # Note: clang will detect the "InstalledDir" based on the path that was used to invoke the tools
+    # This might still have some hidden effects
+    printf '#!/bin/sh\nsr=$(dirname "$(dirname "$(readlink -f "$0")")")\nexec %s -resource-dir="$sr"%s --sysroot="$sr" "$@"\n' "$HOST_CLANG_EXE" "$clangres" > $PREFIX/bin/clang
+    # printf '#!/bin/sh\nsr=$(dirname "$(dirname "$(readlink -f "$0")")")\nexec %s -resource-dir="$sr"%s --sysroot="$sr" "$@"\n' "$(readlink -f "$HOST_CLANG_EXE")" "$clangres" > $PREFIX/bin/clang
+    chmod 755 $PREFIX/bin/clang
+    ln -sf clang $PREFIX/bin/clang++
+    ln -sf clang $PREFIX/bin/clang-cpp
+
+    echo "Using existing clang $HOST_CLANG_EXE ($HOST_CLANG_VER)"
+    $PREFIX/bin/clang -v
+
+    # prefer system llvm installation, but search in llvm private paths (eg. debian does not symlink all tools into /usr/bin)
+    llvmexec="$PATH:$llvmdir/bin"
+
+    for exec in ld.lld llvm-ar llvm-ranlib llvm-nm llvm-objcopy llvm-strip llvm-rc llvm-cvtres \
+                llvm-addr2line llvm-dlltool llvm-readelf llvm-size llvm-strings llvm-addr2line llvm-windres llvm-ml; do
+        execpath=$(PATH=$llvmexec command -v $exec) && ln -sf $execpath $PREFIX/bin/$exec
+    done
+fi
+
 if [ -n "$MACOS_REDIST" ]; then
     : ${MACOS_REDIST_ARCHS:=arm64 x86_64}
     : ${MACOS_REDIST_VERSION:=10.9}