wrappers: Use clang config files for defaults

This makes these defaults more easy to get picked up in various
use cases, when not directly executing a compiler.

wrappers/clang-target-wrapper.sh

@@ -67,20 +67,6 @@ c11)
     FLAGS="$FLAGS -std=c11"
     ;;
 esac
-case $ARCH in
-i686)
-    # Dwarf is the default for i686.
-    ;;
-x86_64)
-    # SEH is the default for x86_64.
-    ;;
-armv7)
-    # SEH is the default for armv7.
-    ;;
-aarch64)
-    # SEH is the default for aarch64.
-    ;;
-esac
 LINKER_FLAGS=""
 case $TARGET_OS in
 mingw32uwp)
@@ -106,11 +92,7 @@ mingw32uwp)
     ;;
 esac
 
-FLAGS="$FLAGS -target $TARGET"
-FLAGS="$FLAGS -rtlib=compiler-rt"
-FLAGS="$FLAGS -unwindlib=libunwind"
-FLAGS="$FLAGS -stdlib=libc++"
-FLAGS="$FLAGS -fuse-ld=lld"
+FLAGS="$FLAGS --config $ARCH-w64-mingw32.cfg"
 FLAGS="$FLAGS --end-no-unused-arguments"
 
 $CCACHE "$CLANG" $FLAGS "$@" $LINKER_FLAGS