cmake: Add ARCH_SIMD_DEFINES variable

It's necessary on ppc64 for plugins that use cmake.

CMakeLists.txt

@@ -129,6 +129,7 @@ if(LOWERCASE_CMAKE_SYSTEM_PROCESSOR MATCHES "(i[3-6]86|x86|x64|x86_64|amd64|e2k)
 	endif()
 elseif(LOWERCASE_CMAKE_SYSTEM_PROCESSOR MATCHES "^(powerpc|ppc)64(le)?")
 	set(NEEDS_SIMDE "0")
+	set(ARCH_SIMD_DEFINES "-DNO_WARN_X86_INTRINSICS")
 	set(ARCH_SIMD_FLAGS "-mvsx")
 	add_compile_definitions(NO_WARN_X86_INTRINSICS)
 else()