config stdc++ for llvm too

Author: vszakats

_build.sh

@@ -1113,21 +1113,24 @@ build_single_target() {
         _CXXFLAGS_GLOBAL+=" -I${tmp}/include/c++/${_TRIPLET}"
         _CXXFLAGS_GLOBAL+=" -I${tmp}/include/c++/backward"
       fi
-    elif [ "${_HOST}" = 'linux' ] && [ "${_OS}" = 'linux' ] && [ "${unamem}" != "${_machine}" ] && [ "${_CC}" = 'llvm' ]; then
-      if [ "${_CRT}" != 'musl' ]; then
-        _CFLAGS_GLOBAL+=" -isystem /usr/${_TRIPLETSH}/include"
-        _LDFLAGS_GLOBAL+=" -L/usr/${_TRIPLETSH}/lib"
-        if [ "${_CCRT}" = 'libgcc' ]; then
-          # https://packages.debian.org/testing/all/libgcc-13-dev-arm64-cross/filelist
-          # /usr/lib/gcc-cross/aarch64-linux-gnu/13/
-          tmp="$(find "/usr/lib/gcc-cross/${_TRIPLETSH}" -mindepth 1 -maxdepth 1 -type d | head -n 1 || true)"
-          if [ -z "${tmp}" ]; then
-            >&2 echo '! Error: Failed to detect gcc-cross env root.'
-            exit 1
+    elif [ "${_HOST}" = 'linux' ] && [ "${_OS}" = 'linux' ] && [ "${unamem}" != "${_machine}" ]; then
+      if [ "${_CC}" = 'llvm' ]; then
+        if [ "${_CRT}" != 'musl' ]; then
+          _CFLAGS_GLOBAL+=" -isystem /usr/${_TRIPLETSH}/include"
+          _LDFLAGS_GLOBAL+=" -L/usr/${_TRIPLETSH}/lib"
+          if [ "${_CCRT}" = 'libgcc' ]; then
+            # https://packages.debian.org/testing/all/libgcc-13-dev-arm64-cross/filelist
+            # /usr/lib/gcc-cross/aarch64-linux-gnu/13/
+            tmp="$(find "/usr/lib/gcc-cross/${_TRIPLETSH}" -mindepth 1 -maxdepth 1 -type d | head -n 1 || true)"
+            if [ -z "${tmp}" ]; then
+              >&2 echo '! Error: Failed to detect gcc-cross env root.'
+              exit 1
+            fi
+            _LDFLAGS_GLOBAL+=" -L${tmp}"
           fi
-          _LDFLAGS_GLOBAL+=" -L${tmp}"
         fi
       fi
+
       if [ "${_DISTRO}" = 'debian' ]; then
         # https://packages.debian.org/testing/all/libstdc++-13-dev-arm64-cross/filelist
         # /usr/aarch64-linux-gnu/include/c++/13/