arm: prevent impossible tail- long-calls with static chain [PR119430]

arm: prevent impossible tail- long-calls with static chain [PR119430]

When a function call uses up all argument registers, and needs IP for
the static chain, there aren't any call-clobbered registers left for
reload to assign as the sibcall target, when -mlong-calls is enabled.
Use the same logic that does the job for indirect calls to prevent
tail calls in this case.

With this change, it is possible to bootstrap armv7a-linux-gnu with
both -O3 and lto, but only with both -mlong-calls and
-ffunction-sections.

Without -mlong-calls, linker veneer thunks may clobber the static
chain register set up by callers in one lto unit, preventing them from
reaching the callee in a separate lto unit.  -ffunction-sections is
required for -mlong-calls to be effective, because both caller and
callee are in the same section, and that disables long-calls when
!flag_reorder_blocks_and_partition.

gcc/ChangeLog

	PR target/119430
	* config/arm/arm.cc (arm_function_ok_for_sibcall): Disable
	sibcalls for long-calls that use all call-clobbered
	general-purpose registers, including the static chain.