cmake: Add -mxsave flag to ARCH_FLAG in BuildParameters.

A couple of users reported compilation issues using gcc 8.2+ on some
machines/distros on github and discord and adding the -mxsave flag
suggested by turtleli seems to fix the issue.

Fixes #2669

cmake/BuildParameters.cmake

@@ -212,7 +212,7 @@ if(${PCSX2_TARGET_ARCHITECTURES} MATCHES "i386")
             # AVX requires some fix of the ABI (mangling) (default 2)
             # Note: V6 requires GCC 4.7
             #set(ARCH_FLAG "-march=native -fabi-version=6")
-            set(ARCH_FLAG "-march=native")
+            set(ARCH_FLAG "-mxsave -march=native")
         endif()
     endif()