Bug 925329 - unify the formatting of xslt ids across 32-bit and 64-bit OSes; r=peterv
Bug 931043 - use AC_TRY_COMPILE to check for how to copy va_args; r=glandium

We shouldn't need to run these programs; compiling them should be enough.

While we're at it, we can remove support for __va_copy, which, AFAICS, is an
old GNU extension and has been superseded by va_copy by anyplace that cares.
Bug 931053 - don't build Mac host tools if --disable-crashreporter; r=ted
Bug 932127 - correctly configure ctypes in cross compilation conditions; r=glandium
Bug 933231 - don't |unset| variables after configuring NSPR; r=ted
Bug 933071 - add --with-macos-private-frameworks to support cross-compiling; r=mshal