include/linux/compiler-gcc.h: sparse can do constant folding of __builtin_bswap*()

Sparse can do constant folding of __builtin_bswap*() since 2017.  Also, a
much recent version of Sparse is needed anyway, see commit 6ec4476a
("Raise gcc version requirement to 4.9").

So, remove the comment about sparse not being yet able to constant fold
__builtin_bswap*() and remove the corresponding test of __CHECKER__.

Link: https://lkml.kernel.org/r/20210226092236.99369-1-luc.vanoostenryck@gmail.com


Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>