Is is possible to put something at the top of the C source file, like
// GCC_OPTIONS=-g,-Wall
that will add those options automatically to
Yes it is, at least for some flags. You can push and pop diagnostic settings like this:
#pragma GCC diagnostic error "-pedantic"
#pragma GCC diagnostic warning "-Wall"
This is also possible for optimization levels on a per-function level:
#pragma GCC optimize ("string"...)
These #pragma definitions affect all code after them in a source file.
See these other questions for more information: