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/aarch64-w64-mingw32.cfg

@@ -0,0 +1,6 @@
+-target aarch64-w64-mingw32
+-rtlib=compiler-rt
+-unwindlib=libunwind
+-stdlib=libc++
+-fuse-ld=lld
+# SEH is the default for aarch64.

wrappers/armv7-w64-mingw32.cfg

@@ -0,0 +1,6 @@
+-target armv7-w64-mingw32
+-rtlib=compiler-rt
+-unwindlib=libunwind
+-stdlib=libc++
+-fuse-ld=lld
+# SEH is the default for armv7.

wrappers/clang-target-wrapper.c

@@ -50,7 +50,7 @@ int _tmain(int argc, TCHAR* argv[]) {
         }
     }
 
-    int max_arg = argc + 22;
+    int max_arg = argc + 18;
     const TCHAR **exec_argv = malloc((max_arg + 1) * sizeof(*exec_argv));
     int arg = 0;
     if (getenv("CCACHE"))
@@ -66,16 +66,6 @@ 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");
@@ -88,12 +78,8 @@ int _tmain(int argc, TCHAR* argv[]) {
         exec_argv[arg++] = _T("-D_UCRT");
     }
 
-    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("--config");
+    exec_argv[arg++] = concat(arch, _T("-w64-mingw32.cfg"));
     exec_argv[arg++] = _T("--end-no-unused-arguments");
 
     for (int i = 1; i < argc; i++)

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

wrappers/i686-w64-mingw32.cfg

@@ -0,0 +1,6 @@
+-target i686-w64-mingw32
+-rtlib=compiler-rt
+-unwindlib=libunwind
+-stdlib=libc++
+-fuse-ld=lld
+# Dwarf is the default for i686.

wrappers/x86_64-w64-mingw32.cfg

@@ -0,0 +1,6 @@
+-target x86_64-w64-mingw32
+-rtlib=compiler-rt
+-unwindlib=libunwind
+-stdlib=libc++
+-fuse-ld=lld
+# SEH is the default for x86_64.