avcodec/x86/vc1dsp_init: Fix build failure with --disable-optimizations and clang

compilers doing DCE at -O0 do not necessarily understand "complex" boolean expressions
Build succeeds with this change, this was the only failure
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/x86/vc1dsp_init.c

@@ -106,10 +106,12 @@ av_cold void ff_vc1dsp_init_x86(VC1DSPContext *dsp)
 {
     int cpu_flags = av_get_cpu_flags();
 
-    if (HAVE_6REGS && INLINE_MMX(cpu_flags) && EXTERNAL_MMX(cpu_flags))
+    if (HAVE_6REGS && INLINE_MMX(cpu_flags))
+        if (EXTERNAL_MMX(cpu_flags))
         ff_vc1dsp_init_mmx(dsp);
 
-    if (HAVE_6REGS && INLINE_MMXEXT(cpu_flags) && EXTERNAL_MMXEXT(cpu_flags))
+    if (HAVE_6REGS && INLINE_MMXEXT(cpu_flags))
+        if (EXTERNAL_MMXEXT(cpu_flags))
         ff_vc1dsp_init_mmxext(dsp);
 
 #define ASSIGN_LF(EXT) \