Windows: Fix ARM64 target detection when using `-A ARM64,version=...` notation.

CMakeLists.txt

@@ -31,7 +31,7 @@ if(CMAKE_SIZEOF_VOID_P EQUAL 8)
 			set(_MEGATEMP_CHECKVAR MSVC_CXX_ARCHITECTURE_ID)
 		endif()
 		# FIXME: Code below also duplicates MEGA_X64 architecture assignment.
-		if(${_MEGATEMP_CHECKVAR} STREQUAL "ARM64")
+		if(${${_MEGATEMP_CHECKVAR}} MATCHES "^ARM64")
 			set(MEGA_ARM64 TRUE)
 			set(MEGA_ARCH ARM64)
 		else()
@@ -145,9 +145,12 @@ if(MSVC)
 				else()
 					set(MEGA_MSVC_VCVARSALL_BAT_ARG "-arch=x86")
 				endif()
-				math(EXPR VS_TOOLCHAIN_VERSION_MAJOR "${VSVERSION} / 10")
-				math(EXPR VS_TOOLCHAIN_VERSION_MINOR "${VSVERSION} % 10")
-				set(MEGA_MSVC_VCVARSALL_BAT_ARG "${MEGA_MSVC_VCVARSALL_BAT_ARG} -vcvars_ver=${VS_TOOLCHAIN_VERSION_MAJOR}.${VS_TOOLCHAIN_VERSION_MINOR}")
+				# If we're using MSVC, then the vcvars_ver can be extracted from the MSVC linker version.
+				# If we're somehow using Clang, then it won't work, but it's fine. VsDevCmd will use highest vcvars_ver available.
+				string(REGEX MATCH "^([0-9]+)\\.([0-9]+)" VSVERSION_MATCH ${CMAKE_C_COMPILER_LINKER_VERSION})
+				if(VSVERSION_MATCH)
+					set(MEGA_MSVC_VCVARSALL_BAT_ARG "${MEGA_MSVC_VCVARSALL_BAT_ARG} -vcvars_ver=${CMAKE_MATCH_1}.${CMAKE_MATCH_2}")
+				endif()
 			else()
 				message(STATUS "Found vcvarsall.bat")
 				if(MEGA_X86)