Fix some configure related build warnings

[Nomis101]

Closes #2265.

This PR will fix the warning
configure: WARNING: unrecognized options: --with-glib
fribidi droped glib dependency in 2017. fribidi/fribidi#14

The PR will fix the warning
configure: WARNING: unrecognized options: --disable-sdl
liboggs configure doesn't know about this option.

The PR suppresses the harmless but annoying warning

  : src/opus_decoder.c:37:10: warning: You appear to be compiling without optimization, if so opus will be very slow. [-W#pragma-messages]
  : # pragma message "You appear to be compiling without optimization, if so opus will be very slow."
  : 
  :          ^
  : 1 warning generated.
  :   CC       src/opus_encoder.lo

Tested on macOS 10.14.

[bradleysepos]

Merged, thanks!