How to handle CFLAG ordering

[Matt Turner]

Hi,

I'm maintaining some ARM/iwMMXt-optimized code in pixman,
http://cgit.freedesktop.org/pixman/

gcc will only emit iwmmxt instructions when -march=iwmmxt{,2} is used,
which is stupid. It also has the side-effect of putting gcc into ARMv5
mode, even though the CPU I care about is ARMv7. So, we want the rest
of the package built with -march=armv7-a.

pixman's build system attempts to compile pixman-mmx.c with
-march=iwmmxt by building it as a convenience library, but when you
build pixman with something like

CFLAGS="-O2 -march=armv7-a -pipe" ./configure

it winds up putting -O2 -march=armv7-a -pipe *after* -march=iwmmxt,
which disables iwmmxt support. There is probably a way to handle this
-- I just don't know how.

The relevant sections of configure.ac and Makefile.am are

http://cgit.freedesktop.org/pixman/tree/configure.ac#n608
http://cgit.freedesktop.org/pixman/tree/pixman/Makefile.am#n93

How can I have automake order the flags such that -march=iwmmxt
appears after the user-specified CFLAGS?

Thanks,
Matt