Revert use of Clang config files

This reverts commit 49db4a3a15,
9f1f0104f1,
4f95c14adf,
c34dc64028,
570fdcd251,
4bff0298c5 and
6939aee0c0.

When relying on Clang config files, two issues appeared:

- Running the compiler-rt tests fails, because the compiler-rt tests
  disable any default config files, breaking the compiler
  in this case:
  https://github.com/llvm/llvm-project/blob/llvmorg-19.1.1/compiler-rt/test/lit.common.cfg.py#L983

- Wine fails to build using llvm-mingw as cross compiler, because
  Wine adds the --no-default-config flag to Clang while compiling,
  if supported:
  https://gitlab.winehq.org/wine/wine/-/blob/wine-9.19/configure.ac?ref_type=tags#L866-868
  This causes llvm-mingw to omit the -rtlib=compiler-rt option
  (specified in a config file), making the compiler look for libgcc
  instead. Doing a check to see that linking succeeds doesn't necessarily
  help here - such a check already exists, but it tests linking with
  -nostdlib -nodefaultlibs:
  https://gitlab.winehq.org/wine/wine/-/blob/wine-9.19/aclocal.m4?ref_type=tags#L193-L206

wrappers/clang-target-wrapper.sh

@@ -67,6 +67,20 @@ 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)
@@ -93,6 +107,10 @@ 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 --end-no-unused-arguments"
 
 $CCACHE "$CLANG" $FLAGS "$@" $LINKER_FLAGS