explicitly assemble all arm asm sources as UAL

these files are all accepted as legacy arm syntax when producing arm
code, but legacy syntax cannot be used for producing thumb2 with
access to the full ISA. even after switching to UAL, some asm source
files contain instructions which are not valid in thumb mode, so these
will need to be addressed separately.

arch/arm/src/arm/atomics.s

+.syntax unified
 .text
 
 .global __a_barrier

crt/arm/crti.s

+.syntax unified
+
 .section .init
 .global _init
 .type _init,%function

crt/arm/crtn.s

+.syntax unified
+
 .section .init
 	pop {r0,lr}
 	bx lr

src/fenv/armhf/fenv.s

+.syntax unified
 .fpu vfp
 
 .global fegetround

src/internal/arm/syscall.s

+.syntax unified
 .global __syscall
 .hidden __syscall
 .type __syscall,%function

src/ldso/arm/dlsym.s

+.syntax unified
 .text
 .global dlsym
 .hidden __dlsym

src/math/armhf/fabs.s

+.syntax unified
 .fpu vfp
 .text
 .global fabs

src/math/armhf/fabsf.s

+.syntax unified
 .fpu vfp
 .text
 .global fabsf

src/math/armhf/sqrt.s

+.syntax unified
 .fpu vfp
 .text
 .global sqrt

src/math/armhf/sqrtf.s

+.syntax unified
 .fpu vfp
 .text
 .global sqrtf

src/setjmp/arm/longjmp.s

+.syntax unified
 .global _longjmp
 .global longjmp
 .type _longjmp,%function

src/setjmp/arm/setjmp.s

+.syntax unified
 .global __setjmp
 .global _setjmp
 .global setjmp

src/signal/arm/restore.s

+.syntax unified
+
 .global __restore
 .type __restore,%function
 __restore:

src/signal/arm/sigsetjmp.s

+.syntax unified
 .global sigsetjmp
 .global __sigsetjmp
 .type sigsetjmp,%function

src/thread/arm/__unmapself.s

+.syntax unified
 .text
 .global __unmapself
 .type   __unmapself,%function

src/thread/arm/clone.s

+.syntax unified
 .text
 .global __clone
 .type   __clone,%function

src/thread/arm/syscall_cp.s

+.syntax unified
 .global __cp_begin
 .hidden __cp_begin
 .global __cp_end