build: avoid frame size error when building without -O2

build: avoid frame size error when building without -O2

libvirt always adds -Werror-frame-larger-than=4096 to the flags when
it builds. When building on Fedora 17, two functions with multiple
1024 buffers declared inside if {} blocks would generate frame size
errors; apparently the version of gcc on Fedora 16 will merge these
multiple buffers into a single buffer even when optimization is off,
but Fedora 17 won't.

The fix is to declare a single 1024 buffer at the top of the two
offending functions, and reuse the single buffer throughout the
functions.