arm: Don't reconfigure globals in arm_configure_build_target

arm: Don't reconfigure globals in arm_configure_build_target

arm_configure_build_target is usually used to reconfigure the
arm_active_target structure, which is then used to reconfigure a
number of other global variables describing the current target.
Occasionally, however, we need to use arm_configure_build_target to
construct a temporary target structure and in that case it is wrong to
try to reconfigure the global variables (although probably harmless,
since arm_option_reconfigure_globals() only looks at
arm_active_target).  At the very least, however, this is wasted work,
so it is best not to do it unless needed.  What's more, several
callers of arm_configure_build target call
arm_option_reconfigure_globals themselves within a few lines, making
the call from within arm_configure_build_target completely redundant.

So this patch moves the responsibility of calling of
arm_configure_build_target to its callers (only two places needed
updating).

gcc:
	* config/arm/arm.c (arm_configure_build_target): Don't call
	arm_option_reconfigure_globals.
	(arm_option_restore): Call arm_option_reconfigure_globals after
	reconfiguring the target.
	* config/arm/arm-c.c (arm_pragma_target_parse): Likewise.
(cherry picked from commit 6a37d0331c25f23628d4308e5a75624005c223b2)