prefixing This adds an API to set optimization options externally,
providing an alternative and general solution for the non-portable
run-time tests used by the ARM Neon code. It also makes those tests
compile and link on Android.
The order of settings vs options in pnglibconf.h is reversed to allow
settings to depend on options and options can now set (or override) the
defaults for settings.
source files. This change might make the check for a special C preprocessor
unnecessary, and it also eliminates the requirement for sed in the
configure build process. NOTE: this is incomplete, a change must also
be made to pnglibconf.mak
