[HWASan] Use a single .weak binding in asm.

[morehouse]

Summary

Specifying .global and .weak causes a compiler warning:

`warning: __sigsetjmp changed binding to STB_WEAK`

Specifying only .weak should have the same effect without causing a
warning.

[eugenis]

Sure.
Of course, this is not clearly documented anywhere.
LGTM

[MaskRay]

ELF has 3 main bindings: STB_LOCAL, STB_GLOBAL, STB_WEAK.
.local .globa?l .weak control them.
They are conceptually mutual exclusive.

The integrated assembler used to treat .weak .globl differently from GNU as .globl .weak.
To warn users about the potentially unintended consequence, MC started to warn.

compiler-rt/lib/hwasan/hwasan_setjmp_aarch64.S

__interceptor_sigsetjmp:
   // We always have the second argument to __sigjmp_save (savemask) set, since
   // the _setjmp function above has set it for us as `false`.
   // This function is defined in hwasan_interceptors.cc
   b __sigjmp_save
   CFI_ENDPROC
 ASM_SIZE(__interceptor_sigsetjmp)
 
 
-.macro ALIAS first second
-  .globl \second
+.macro WEAK_ALIAS first second
+  .weak \second
   .equ \second\(), \first
 .endm
 
 #if SANITIZER_ANDROID
-ALIAS __interceptor_sigsetjmp, sigsetjmp
-.weak sigsetjmp
-
-ALIAS __interceptor_setjmp_bionic, setjmp
-.weak setjmp
+WEAK_ALIAS __interceptor_sigsetjmp, sigsetjmp
+WEAK_ALIAS __interceptor_setjmp_bionic, setjmp
 #else
-ALIAS __interceptor_sigsetjmp, __sigsetjmp
-.weak __sigsetjmp
+WEAK_ALIAS __interceptor_sigsetjmp, __sigsetjmp
 #endif
 
-ALIAS __interceptor_setjmp, _setjmp
-.weak _setjmp
+WEAK_ALIAS __interceptor_setjmp, _setjmp
 #endif
 
 // We do not need executable stack.
 NO_EXEC_STACK_DIRECTIVE
 
 GNU_PROPERTY_BTI_PAC

compiler-rt/lib/hwasan/hwasan_setjmp_x86_64.S

__interceptor_sigsetjmp:
 
   jmp __sigjmp_save
 
   CFI_ENDPROC
 ASM_SIZE(__interceptor_sigsetjmp)
 
 
 .macro WEAK_ALIAS first second
-  .globl \second
-  .equ \second\(), \first
   .weak \second
+  .equ \second\(), \first
 .endm
 
 WEAK_ALIAS __interceptor_sigsetjmp, __sigsetjmp
 WEAK_ALIAS __interceptor_setjmp, _setjmp
 #endif
 
 // We do not need executable stack.
 NO_EXEC_STACK_DIRECTIVE