Without this flag -Wall generates warnings that nobody wants to see fixed or
worked around. Disabling those warnings is thus the best solution.
Originally committed as revision 24666 to svn://svn.ffmpeg.org/ffmpeg/trunk
# add some useful compiler flags if supported
check_cflags -Wdeclaration-after-statement
check_cflags -Wall
+check_cflags -Wno-parentheses
check_cflags -Wno-switch
check_cflags -Wdisabled-optimization
check_cflags -Wpointer-arith