configure: add spirv_compiler to avcodec_suggest

893f3fde4c made libavcodec link to libshaderc/libglslang, though
no codecs depend on it at this immediate moment.

This was merged largely as a coordination effort to synchronize three
different developers' repositories to allow them to send patches without
overlapping functionality in between.

This line can be removed once the first component to depend on spirv_compiler
lands, but leaving it in is fine too.

configure

@@ -4039,7 +4039,7 @@ cws2fws_extralibs="zlib_extralibs"
 
 # libraries, in any order
 avcodec_deps="avutil"
-avcodec_suggest="libm stdatomic"
+avcodec_suggest="libm stdatomic spirv_compiler"
 avdevice_deps="avformat avcodec avutil"
 avdevice_suggest="libm stdatomic"
 avfilter_deps="avutil"