Revert "Add feature flags and missing #includes."

This reverts commit dd5fa236ae.

Also, set `-std=gnu99` in Bazel build.

src/audio_call.c

@@ -41,7 +41,6 @@
 #include <stdbool.h>
 #include <curses.h>
 #include <string.h>
-#include <strings.h>
 #include <pthread.h>
 #include <unistd.h>
 #include <stdlib.h>