Fix aarch64 windows detection

src/Makevars

@@ -9,10 +9,10 @@ else
 	DLL := .so
 endif
 
-CC_VERSION :=  $(shell $(CC) -dumpfullversion -dumpversion 2>&1)
+CC_VERSION :=  $(shell $(CXX) -dumpfullversion -dumpversion 2>&1)
 CC_MAJOR := $(word 1,$(subst ., ,$(CC_VERSION)))
 
-CLANG_CHECK := $(shell echo | $(CC) -dM -E - | grep -i __clang__)
+CLANG_CHECK := $(shell echo | $(CXX) -dM -E - | grep -i __clang__)
 
 # Older versions of gcc and clang don't provide the stdatomic.h header
 ifneq (,$(CLANG_CHECK))
@@ -21,7 +21,7 @@ ifneq (,$(CLANG_CHECK))
 	endif
 # Clang on armel needs libatomic
 	ifeq ($(shell uname -m), armv7l)
-	  CC_TARGET := $(shell $(CC) -v 2>&1 | grep Target | cut -d ' ' -f 2)
+	  CC_TARGET := $(shell $(CXX) -v 2>&1 | grep Target | cut -d ' ' -f 2)
 		ifeq ($(findstring gnueabihf,$(CC_TARGET)),)
 			PKG_LIBS += -latomic
 		endif