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when invoking the assembler, arm gcc does not always pass the right
flags to enable use of vfp instruction mnemonics. for C code it
produces, it emits the .fpu directive, but this does not help when
building asm source files, which tlsdesc needs to be. to fix, use an
explicit directive here.
commit 0beb9dfbecad38af9759b1e83eeb007e28b70abb introduced this
regression. it has not appeared in any release.
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the indirect function call is a significant portion of the code path
for the dynamic case, and most users are probably building for ISA
levels where it can be omitted.
we could drop at least one register save/restore (lr) with this
change, and possibly another (ip) with some clever shuffling, but it's
not clear whether there's a way to do it that's not more expensive, or
whether avoiding the save/restore would have any practical effect, so
in the interest of avoiding complexity it's omitted for now.
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unlike other asm where the baseline ISA is used, these functions are
hot paths and use ISA-level specializations.
call-clobbered vfp registers are saved before calling __tls_get_new,
since there is no guarantee it won't use them. while setjmp/longjmp
have to use hwcap to decide whether to the fpu is in use, since
application code could be using vfp registers even if libc was
compiled as pure softfloat, __tls_get_new is part of libc and can be
assumed not to have access to vfp registers if tlsdesc.S does not.
thus it suffices just to check the predefined preprocessor macros. the
check for __ARM_PCS_VFP is redundant; !__SOFTFP__ must always be true
if the target ISA level includes fpu instructions/registers.
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