swscale: try to use mmap only if available

Some systems, e.g. Minix, have sys/mman.h defining MAP_ANONYMOUS without
providing (working) mmap and friends.  The mmx filter generation code
checks only for MAP_ANONYMOUS, not for availability of mmap itself which
leads to build errors on aforementioned systems.

This changes the conditional compilation to use mmap only if all the
required functions are available.
Signed-off-by: Mans Rullgard <mans@mansr.com>

libswscale/utils.c

@@ -1018,6 +1018,8 @@ av_cold int sws_init_context(SwsContext *c, SwsFilter *srcFilter,
         }
     }
 
+#define USE_MMAP (HAVE_MMAP && HAVE_MPROTECT && defined MAP_ANONYMOUS)
+
     /* precalculate horizontal scaler filter coefficients */
     {
 #if HAVE_MMXEXT_INLINE
@@ -1028,7 +1030,7 @@ av_cold int sws_init_context(SwsContext *c, SwsFilter *srcFilter,
             c->chrMmx2FilterCodeSize = initMMX2HScaler(c->chrDstW, c->chrXInc,
                                                        NULL, NULL, NULL, 4);
 
-#ifdef MAP_ANONYMOUS
+#if USE_MMAP
             c->lumMmx2FilterCode = mmap(NULL, c->lumMmx2FilterCodeSize, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
             c->chrMmx2FilterCode = mmap(NULL, c->chrMmx2FilterCodeSize, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 #elif HAVE_VIRTUALALLOC
@@ -1051,7 +1053,7 @@ av_cold int sws_init_context(SwsContext *c, SwsFilter *srcFilter,
             initMMX2HScaler(c->chrDstW, c->chrXInc, c->chrMmx2FilterCode,
                             c->hChrFilter, c->hChrFilterPos, 4);
 
-#ifdef MAP_ANONYMOUS
+#if USE_MMAP
             mprotect(c->lumMmx2FilterCode, c->lumMmx2FilterCodeSize, PROT_EXEC | PROT_READ);
             mprotect(c->chrMmx2FilterCode, c->chrMmx2FilterCodeSize, PROT_EXEC | PROT_READ);
 #endif
@@ -1630,7 +1632,7 @@ void sws_freeContext(SwsContext *c)
     av_freep(&c->hChrFilterPos);
 
 #if HAVE_MMX_INLINE
-#ifdef MAP_ANONYMOUS
+#if USE_MMAP
     if (c->lumMmx2FilterCode)
         munmap(c->lumMmx2FilterCode, c->lumMmx2FilterCodeSize);
     if (c->chrMmx2FilterCode)