... and fix the compile errors from it I get on my build.
It's Cairo style to put declarations before the code, so better warn
about it.
Besides, it eases porting to old compilers like MSVC.
We don't actually check that -Wno-attribute does what
we think it does. On clang it doesn't since it happily
seems to recognize but ignore the attribute.
This patch factors out a silent version of CAIRO_CC_TRY_FLAG
which accepts an optional program argument and actually tests
that the compiler doesn't produce any warning messages. It
is then used to check that -Wno-attribute doesn't complain
when the __warn_unused_result__ attribute is applied to
void functions or variables.
Richard Hult reported that -Wl,--allow-shlib-undefined was incorrectly
being identified as supported by gcc under Mac OS/X:
configure:25103: checking whether gcc supports -Wl,--allow-shlib-undefined
configure:25117: gcc -c -Werror -Wl,--allow-shlib-undefined conftest.c
>&5
i686-apple-darwin9-gcc-4.0.1: --allow-shlib-undefined: linker input file
unused because linking not done
So instead of just checking whether the compiler accepts the flag, check
that we can actually link a dummy file.
If the native windowing system is disable (e.g. --disable-xlib) then the
test suite fails to build since the vector converters typically depend
upon gdk-pixbuf-2.0, which in turn depends upon a native gdk which
requires cairo to be built with support for the native windowing system. A
mess that should be resolved by separating rsvg and poppler into core and
higher-level libraries, but which we can workaround by simply ignoring
errors from undefined functions at link time.
