OvmfPkg: Don't add -mno-mmx -mno-sse option for XCODE5 tool chain
Ovmf appended option -mno-mmx -mno-sse, but these two options were enabled
in Openssl. The compiler option becomes -mmmx ?msse -mno-mmx -mno-sse. It
trig mac clang compiler hang when compile one source file in openssl.
This issue is found when SECURE_BOOT_ENABLE is TRUE. This may be the compiler
issue. To work around it, don't add these two options for XCODE5 tool chain.