config.mak.uname: add support for clangarm64

CLANGARM64 is a relatively new MSYSTEM added by the MSYS2 team. In order
to have Git build correctly for this platform, let's add some
configuration for it to config.mak.uname.

Signed-off-by: Dennis Ameling <dennis@dennisameling.com>

Author: dennisameling

config.mak.uname

@@ -711,6 +711,10 @@ else
 			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