configure: Add -lrt dependency to avutil's pc file.

This is needed for clock_gettime.
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

configure

@@ -4053,7 +4053,7 @@ check_func  ${malloc_prefix}memalign            && enable memalign
 check_func  ${malloc_prefix}posix_memalign      && enable posix_memalign
 
 check_cpp_condition unistd.h "defined(_POSIX_MONOTONIC_CLOCK)" &&
-    check_func_headers time.h clock_gettime || { check_func_headers time.h clock_gettime -lrt && add_extralibs -lrt; }
+    check_func_headers time.h clock_gettime || { check_func_headers time.h clock_gettime -lrt && add_extralibs -lrt && LIBRT="-lrt"; }
 
 check_func  fcntl
 check_func  fork
@@ -4838,7 +4838,7 @@ Cflags: -I\${includedir}
 EOF
 }
 
-pkgconfig_generate libavutil     "Libav utility library"          "$LIBAVUTIL_VERSION"     "$LIBM"
+pkgconfig_generate libavutil     "Libav utility library"          "$LIBAVUTIL_VERSION"     "$LIBRT $LIBM"
 pkgconfig_generate libavcodec    "Libav codec library"            "$LIBAVCODEC_VERSION"    "$extralibs"
 pkgconfig_generate libavformat   "Libav container format library" "$LIBAVFORMAT_VERSION"   "$extralibs"
 pkgconfig_generate libavdevice   "Libav device handling library"  "$LIBAVDEVICE_VERSION"   "$extralibs"