Remove m4/fontforge_compiler_flags.m4 and do it in configure.ac

Program simplification by moving AX_CHECK_COMPILE_FLAG() into configure.ac
to make it easier to follow program logic.
remove line between "#ifndef _FF_CONFIG_H" and "#define _FF_CONFIG_H 1"
Delete m4/fontforge_my_flags_and_libs.m4 for simplification's sake

Move away from mental gymnastics of having to look in other files for
info and simply put these variables where configure.ac makes use of them.