nss: move Darwin stuff from nss.patch to nss_macosx.patch

Change-Id: I5fc7cdbcdf079edb101f6a8c3851c4cf4f92e258
nss: remove permission changes from nss_macosx.patch

... and instead do that in ExternalProject, which should be more
maintainable than patching.

Change-Id: I0ccf5697976399cf4f92c53e896492044ee6492d
GCC diagnostic push / pop requires HAVE_GCC_PRAGMA_DIAGNOSTIC_SCOPE

Change-Id: I0765649b94b370caf92a29a8ff2224e335196612
connectivity: remove #pragma GCC system_header in mozabdrv

... which can only be built with MSVC currently anyway.

Change-Id: I806be27ec18e4f04e000f0b5d9ea613c3199855c
boost: stop using #pragma GCC system_header

... it breaks dependency generation.

Change-Id: Ib6e1dac1210020d3a6eb1748f1266e69582f199e
clucene: stop using #pragma GCC system_header

... it breaks dependency generation.

Change-Id: I992e47ecea697617820358f711b7a6408fdabbe3
neon: stop using #pragma GCC system_header

... it breaks dependency generation.

Change-Id: I524f1789c32a633e8930a4e36a893ce02de66390
vigra: stop using #pragma GCC system_header

... don't even get any warning with that removed.

Change-Id: I2647a5951a4ac3cba174a3564e99ef81e4959992