osdep: add MP_UNREACHABLE

This seems to work on gcc, clang and mingw as-is, but I made it
conditional on __GNUC__ just in case, even though I can't figure out
which compilers we care about that don't export this define.

Also replace all instances of assert(0) in the code by MP_UNREACHABLE(),
which is a strict improvement.

3 files changed, 3 insertions, 3 deletions

diff --git a/video/mp_image.c b/video/mp_image.c
index 0e95a59808..e8d433cbfe 100644
--- a/video/mp_image.c
+++ b/video/mp_image.c
@@ -593,7 +593,7 @@ static bool endian_swap_bytes(void *d, size_t bytes, size_t word_size)
             AV_WL32(ud + x * 2, AV_RB32(ud + x * 2));
         break;
     default:
-        assert(0);
+        MP_UNREACHABLE();
     }
 
     return true;
diff --git a/video/out/gpu/video.c b/video/out/gpu/video.c
index 5d6b766d36..43fff511a1 100644
--- a/video/out/gpu/video.c
+++ b/video/out/gpu/video.c
@@ -4237,7 +4237,7 @@ static void gl_video_dr_free_buffer(void *opaque, uint8_t *data)
         }
     }
     // not found - must not happen
-    assert(0);
+    MP_UNREACHABLE();
 }
 
 struct mp_image *gl_video_get_image(struct gl_video *p, int imgfmt, int w, int h,
diff --git a/video/repack.c b/video/repack.c
index ed78981b3c..7973208caf 100644
--- a/video/repack.c
+++ b/video/repack.c
@@ -169,7 +169,7 @@ static void swap_endian(struct mp_image *dst, int dst_x, int dst_y,
                     ((uint32_t *)d)[x] = av_bswap32(((uint32_t *)s)[x]);
                 break;
             default:
-                assert(0);
+                MP_UNREACHABLE();
             }
         }
     }