Set default optimization level to -xO4 for Solaris/Forte builds.

Thanks to Roland Mainz <Roland.Mainz@informatik.med.uni-giessen.de> for the patch.
Bug #109860 r=cls

configure.in

@@ -1254,6 +1254,7 @@ dnl the qsort routine under solaris is faulty
        NS_USE_NATIVE=1
        AC_DEFINE(NSCAP_DISABLE_DEBUG_PTR_TYPES)
        LDFLAGS="-xildoff -zlazyload -zcombreloc $LDFLAGS"
+       MOZ_OPTIMIZE_FLAGS="-xO4"
        MKSHLIB='$(CXX) $(CXXFLAGS) $(DSO_PIC_FLAGS) $(DSO_LDOPTS) -o $@'
        MKCSHLIB='$(CC) $(CFLAGS) $(DSO_PIC_FLAGS) $(DSO_LDOPTS) -o $@'
        MKSHLIB_FORCE_ALL='-Qoption ld -z,allextract'