Fix Alpine/musl test-suite blockers: busybox diff, aarch64 wchar_t

- runtests.sh used diff --strip-trailing-cr unconditionally; busybox
  diff (Alpine) lacks that option, so every .expect comparison errored
  and counted as a mismatch.  Probe for the option once.

- c2mir's builtin aarch64 stddef.h declared 'typedef int wchar_t;', but
  wchar_t is unsigned int in AAPCS64 (and caarch64.h already says
  MIR_WCHAR_MIN 0).  glibc never notices because its headers trust the
  compiler's stddef.h, but musl's bits/alltypes.h redeclares wchar_t
  per-arch ('typedef unsigned wchar_t;'), making every program that
  includes both fail with 'repeated declaration wchar_t' - this broke
  the c2m bootstrap on Alpine aarch64.  Keep int on Apple (signed
  there), and fix the __WCHAR_MAX__/__WCHAR_MIN__ predefines on Linux
  to match gcc (4294967295u / 0u).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: cyanogilvie

c-tests/runtests.sh

@@ -34,6 +34,13 @@ else
     ARCH="other"
 fi
 
+# busybox diff (e.g. on Alpine) lacks --strip-trailing-cr
+if diff --strip-trailing-cr /dev/null /dev/null >/dev/null 2>&1;then
+    DIFF_STRIP_CR=--strip-trailing-cr
+else
+    DIFF_STRIP_CR=
+fi
+
 runtest () {
 	t=$1
 	if test -f $t.mach && ! $GREP -E "`uname -m`" $t.mach >/dev/null; then
@@ -57,14 +64,14 @@ runtest () {
 	$TIMEOUT sh $execution_program $compiler $t $add_main 2>$stderrf >$outf
 	code=$?
 	if test $code = $expect_code; then
-	    if test x$expect_out != x && ! diff --strip-trailing-cr -up $expect_out $outf >$errf;then
+	    if test x$expect_out != x && ! diff $DIFF_STRIP_CR -up $expect_out $outf >$errf;then
 	            $ECHO Output mismatch
 		    cat $errf
             else
 		    ok=`expr $ok + 1`
 	            $ECHO -ne "OK               \r"
 	    fi
-	    if test x$stderr_expect_out != x && ! diff --strip-trailing-cr -up $stderr_expect_out $stderrf >$errf;then
+	    if test x$stderr_expect_out != x && ! diff $DIFF_STRIP_CR -up $stderr_expect_out $stderrf >$errf;then
 	            $ECHO Stderr mismatch
 		    cat $errf
             else

c2mir/aarch64/mirc_aarch64_linux.h

@@ -52,11 +52,13 @@ static char aarch64_mirc[]
     "#define __UINT32_MAX__ (__INT32_MAX__ * 2u + 1u)\n"
     "#define __UINT64_MAX__ (__INT64_MAX__ * 2u + 1u)\n"
 #if defined(__linux__)
-    "#define __WCHAR_MAX__ 0x7fffffff\n"
+    /* wchar_t is unsigned int in AAPCS64 */
+    "#define __WCHAR_MAX__ 4294967295u\n"
+    "#define __WCHAR_MIN__ 0u\n"
 #else
     "#define __WCHAR_MAX__ 2147483647\n"
-#endif
     "#define __WCHAR_MIN__ (-__WCHAR_MAX__ - 1)\n"
+#endif
     "#define __SCHAR_MAX__ __INT8_MAX__\n"
     "#define __SHRT_MAX__ __INT16_MAX__\n"
     "#define __INT_MAX__ __INT32_MAX__\n"

c2mir/aarch64/mirc_aarch64_stddef.h

@@ -10,7 +10,12 @@ static char stddef_str[]
     "typedef long ptrdiff_t;\n"
     "typedef unsigned long size_t;\n"
     "typedef long double max_align_t;\n"
+#if defined(__APPLE__)
     "typedef int wchar_t;\n"
+#else
+    /* unsigned in AAPCS64; matters because musl's alltypes.h redeclares it */
+    "typedef unsigned int wchar_t;\n"
+#endif
     "\n"
     "#define NULL ((void *) 0)\n"
     "\n"