Merge branch 'js/windows-arm64' into jch

Update to arm64 Windows port.

* js/windows-arm64:
  max_tree_depth: lower it for clangarm64 on Windows
  mingw(arm64): do move the `/etc/git*` location
  msvc: do handle builds on Windows/ARM64
  mingw: do not use nedmalloc on Windows/ARM64
  config.mak.uname: add support for clangarm64
  bswap.h: add support for built-in bswap functions

compat/bswap.h

@@ -35,7 +35,19 @@ static inline uint64_t default_bswap64(uint64_t val)
 #undef bswap32
 #undef bswap64
 
-#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
+/**
+ * __has_builtin is available since Clang 10 and GCC 10.
+ * Below is a fallback for older compilers.
+ */
+#ifndef __has_builtin
+	#define __has_builtin(x) 0
+#endif
+
+#if __has_builtin(__builtin_bswap32) && __has_builtin(__builtin_bswap64)
+#define bswap32(x) __builtin_bswap32((x))
+#define bswap64(x) __builtin_bswap64((x))
+
+#elif defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
 
 #define bswap32 git_bswap32
 static inline uint32_t git_bswap32(uint32_t x)

config.mak.uname

@@ -439,7 +439,11 @@ ifeq ($(uname_S),Windows)
         ifeq (MINGW32,$(MSYSTEM))
 		prefix = /mingw32
         else
-		prefix = /mingw64
+                ifeq (CLANGARM64,$(MSYSTEM))
+			prefix = /clangarm64
+                else
+			prefix = /mingw64
+                endif
         endif
 	# Prepend MSVC 64-bit tool-chain to PATH.
 	#
@@ -492,7 +496,7 @@ ifeq ($(uname_S),Windows)
 	NO_POSIX_GOODIES = UnfortunatelyYes
 	NATIVE_CRLF = YesPlease
 	DEFAULT_HELP_FORMAT = html
-ifeq (/mingw64,$(subst 32,64,$(prefix)))
+ifeq (/mingw64,$(subst 32,64,$(subst clangarm,mingw,$(prefix))))
 	# Move system config into top-level /etc/
 	ETC_GITCONFIG = ../etc/gitconfig
 	ETC_GITATTRIBUTES = ../etc/gitattributes
@@ -731,6 +735,10 @@ ifeq ($(uname_S),MINGW)
 		prefix = /mingw64
 		HOST_CPU = x86_64
 		BASIC_LDFLAGS += -Wl,--pic-executable,-e,mainCRTStartup
+        else ifeq (CLANGARM64,$(MSYSTEM))
+		prefix = /clangarm64
+		HOST_CPU = aarch64
+		BASIC_LDFLAGS += -Wl,--pic-executable,-e,mainCRTStartup
         else
 		COMPAT_CFLAGS += -D_USE_32BIT_TIME_T
 		BASIC_LDFLAGS += -Wl,--large-address-aware
@@ -745,8 +753,10 @@ ifeq ($(uname_S),MINGW)
 	HAVE_LIBCHARSET_H = YesPlease
 	USE_GETTEXT_SCHEME = fallthrough
 	USE_LIBPCRE = YesPlease
-	USE_NED_ALLOCATOR = YesPlease
-        ifeq (/mingw64,$(subst 32,64,$(prefix)))
+        ifneq (CLANGARM64,$(MSYSTEM))
+		USE_NED_ALLOCATOR = YesPlease
+        endif
+        ifeq (/mingw64,$(subst 32,64,$(subst clangarm,mingw,$(prefix))))
 		# Move system config into top-level /etc/
 		ETC_GITCONFIG = ../etc/gitconfig
 		ETC_GITATTRIBUTES = ../etc/gitattributes

environment.c

@@ -81,6 +81,16 @@ int max_allowed_tree_depth =
 	 * the stack overflow can occur.
 	 */
 	512;
+#elif defined(GIT_WINDOWS_NATIVE) && defined(__clang__) && defined(__aarch64__)
+	/*
+	 * Similar to Visual C, it seems that on Windows/ARM64 the clang-based
+	 * builds have a smaller stack space available. When running out of
+	 * that stack space, a `STATUS_STACK_OVERFLOW` is produced. When the
+	 * Git command was run from an MSYS2 Bash, this unfortunately results
+	 * in an exit code 127. Let's prevent that by lowering the maximal
+	 * tree depth; This value seems to be low enough.
+	 */
+	1280;
 #else
 	2048;
 #endif