Try to fix autoconf madness for bug 530896.

js/src/configure.in

@@ -2478,38 +2478,35 @@ fi
 
 dnl Configure SSE2 support
 
-dnl Enable SSE2 support in the compiler if available.
-dnl ========================================================
+HAVE_SSE2=
+MUST_DETECT_SSE2=
 case "$target" in
-i?86-*|x86_64*-*)
+i?86-*)
+    HAVE_SSE2=1
+    case "$target_os" in
+    darwin*)
+        ;;
+    *)
+        MUST_DETECT_SSE2=1
+        ;;
+    esac
+    ;;
+x86_64*-*)e
+    HAVE_SSE2=1
+    ;;
+esac
+
+if test "$HAVE_SSE2"; then
+    AC_DEFINE(HAVE_SSE2)
     if test "$GNU_CC"; then
         CFLAGS="$CFLAGS -msse2"
     fi
     if test "$GNU_CXX"; then
         CXXFLAGS="$CXXFLAGS -msse2"
     fi
-    ;;
-esac
-
-dnl If we have the proper include file, enable SSE2 support.
-dnl ========================================================
-HAVE_SSE2=
-AC_CHECK_HEADER(xmmintrin.h, HAVE_SSE2=1)
-AC_CHECK_HEADER(emmintrin.h, HAVE_SSE2=1 && AC_DEFINE(USE_EMM_INTRIN))
-
-if test "$HAVE_SSE2"; then
-    AC_DEFINE(HAVE_SSE2)
-    case "$target_os" in
-    darwin*)
-        ;;
-    *)
-        case "$target" in
-        i?86-*)
-            AC_DEFINE(MUST_DETECT_SSE2)
-            ;;
-        esac
-        ;;
-    esac
+    if test "$MUST_DETECT_SSE2"; then
+        AC_DEFINE(MUST_DETECT_SSE2)
+    fi
 fi
 
 dnl Configure JIT support

js/src/jsnum.h

@@ -48,10 +48,10 @@
 #include <ieeefp.h>
 #endif
 #ifdef HAVE_SSE2
-#ifdef USE_EMM_INTRIN
-#include <emmintrin.h>
-#else
+#ifdef __GNUC__
 #include <xmmintrin.h>
+#else
+#include <emmintrin.h>
 #endif
 #endif