Enable the additional GCC compiler flags on all systems.

There was no reason to add more flags only on Linux/Hurd; in fact, in
kdelibs' FindKDE4Internal.cmake there's also a block with similar
settings for the BSDs.

Make it more general by removing the system checks before setting
these flags. -Wno-long-long is particularly needed when one is
building code with -pedantic (see picmi, for example).

CCMAIL: kde-buildsystem@kde.org