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.c

@@ -50,7 +50,7 @@ int _tmain(int argc, TCHAR* argv[]) {
         }
     }
 
-    int max_arg = argc + 18;
+    int max_arg = argc + 22;
     const TCHAR **exec_argv = malloc((max_arg + 1) * sizeof(*exec_argv));
     int arg = 0;
     if (getenv("CCACHE"))
@@ -66,6 +66,16 @@ int _tmain(int argc, TCHAR* argv[]) {
     else if (!_tcscmp(exe, _T("c11")))
         exec_argv[arg++] = _T("-std=c11");
 
+    if (!_tcscmp(arch, _T("i686"))) {
+        // Dwarf is the default for i686.
+    } else if (!_tcscmp(arch, _T("x86_64"))) {
+        // SEH is the default for x86_64.
+    } else if (!_tcscmp(arch, _T("armv7"))) {
+        // SEH is the default for armv7.
+    } else if (!_tcscmp(arch, _T("aarch64"))) {
+        // SEH is the default for aarch64.
+    }
+
     if (target_os && !_tcscmp(target_os, _T("mingw32uwp"))) {
         // the UWP target is for Windows 10
         exec_argv[arg++] = _T("-D_WIN32_WINNT=0x0A00");
@@ -80,6 +90,10 @@ int _tmain(int argc, TCHAR* argv[]) {
 
     exec_argv[arg++] = _T("-target");
     exec_argv[arg++] = target;
+    exec_argv[arg++] = _T("-rtlib=compiler-rt");
+    exec_argv[arg++] = _T("-unwindlib=libunwind");
+    exec_argv[arg++] = _T("-stdlib=libc++");
+    exec_argv[arg++] = _T("-fuse-ld=lld");
     exec_argv[arg++] = _T("--end-no-unused-arguments");
 
     for (int i = 1; i < argc; i++)