Don't use SSE2 instructions on Haiku.

We still support older architectures, so we don't want this. Since the
env CXXFLAGS are appended to the one set in the cmake files, there is no
way to force this in the CMake project.

Tools/Scripts/webkitdirs.pm

@@ -1955,7 +1955,7 @@ sub generateBuildSystemFromCMakeProject
     # Compiler options to keep floating point values consistent
     # between 32-bit and 64-bit architectures.
     determineArchitecture();
-    if ($architecture ne "x86_64" && !isARM() && !isCrossCompilation()) {
+    if ($architecture ne "x86_64" && !isARM() && !isCrossCompilation() && !isHaiku()) {
         $ENV{'CXXFLAGS'} = "-march=pentium4 -msse2 -mfpmath=sse " . ($ENV{'CXXFLAGS'} || "");
     }