Fix iOS simulator build after 1f0823c (Rewrite simd.prf to share more code)

Now that we rely on simd.prf for all SIMD sources (including NEON and SSE2),
we need to ensure that CONFIG has the right SIMD values to match simulator.

This worked before due to us checking QT_CPU_FEATURES.$$QT_ARCH and adding
directly to SOURCES.

Change-Id: I4ea7f559e83860eabff1948ad5d140bbb65454df
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

mkspecs/macx-ios-clang/features/default_pre.prf

@@ -16,4 +16,6 @@ iphonesimulator_and_iphoneos:iphonesimulator {
     QT_ARCH = i386
     QT_CPU_FEATURES.i386 = sse sse2
     DEFINES += QT_COMPILER_SUPPORTS_SSE2
+    CONFIG -= neon
+    CONFIG += sse sse2
 }