Add SystemProcessor option to CMakeLists.txt to make cross compiling …

…easier.

CMakeLists.txt

@@ -59,6 +59,8 @@ cmake_dependent_option(BuildSymbolServer "Build WIP Windows Symbol Server (exper
 # Note that we always use the bundled copy of minizip, since it is modified to
 # use Z_Malloc.
 
+set(SystemProcessor "${CMAKE_SYSTEM_PROCESSOR}" CACHE STRING "Option to override CMAKE_SYSTEM_PROCESSOR")
+
 set(UseInternalOpenALDefault OFF)
 set(UseInternalZlibDefault   OFF)
 set(UseInternalPNGDefault    OFF)
@@ -113,28 +115,28 @@ if(WIN32)
 	endif()
 else()
 	set(X86 OFF)
-	if(CMAKE_SYSTEM_PROCESSOR MATCHES "^(arm64|aarch64)$")
+	if(SystemProcessor MATCHES "^(arm64|aarch64)$")
 		set(Architecture "arm64")
 		add_definitions(-DPNG_ARM_NEON_OPT=0)
-	elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "^arm")
+	elseif(SystemProcessor MATCHES "^arm")
 		set(Architecture "arm")
-	elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "^i.86$")
+	elseif(SystemProcessor MATCHES "^i.86$")
 		set(X86 ON)
 		if(APPLE)
 			set(Architecture "x86")
 		else()
 			# e.g. Linux
 			set(Architecture "i386")
 		endif()
-	elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "^x86.64$")
+	elseif(SystemProcessor MATCHES "^x86.64$")
 		set(X86 ON)
 		set(Architecture "x86_64")
-	elseif(CMAKE_SYSTEM_PROCESSOR STREQUAL "powerpc")
+	elseif(SystemProcessor STREQUAL "powerpc")
 		set(Architecture "ppc")
-	elseif(CMAKE_SYSTEM_PROCESSOR STREQUAL "powerpc64")
+	elseif(SystemProcessor STREQUAL "powerpc64")
 		set(Architecture "ppc64")
 	else()
-		set(Architecture "${CMAKE_SYSTEM_PROCESSOR}")
+		set(Architecture "${SystemProcessor}")
 	endif()
 endif()