arm64: Adjust mem*.S to use WEAK instead of .weak.

Commit 39d114d added .weak directives to
support KASAN on AArch64, however this breaks support for LLVM's
integrated assembler as LLVM switched the .weak directive to produce a
STB_GLOBAL binding rather than STB_WEAK [1].

By utilising the WEAK macro instead, both LLVM and GCC will produce a
STB_WEAK binding.

[1] : https://reviews.llvm.org/D90108

Link: ClangBuiltLinux/linux#1190
Signed-off-by: Diab Neiroukh <lazerl0rd@thezest.dev>

arch/arm64/lib/memcpy.S

@@ -68,9 +68,8 @@
 	stp \ptr, \regB, [\regC], \val
 	.endm
 
-	.weak memcpy
 ENTRY(__memcpy)
-ENTRY(memcpy)
+WEAK(memcpy)
 #include "copy_template.S"
 	ret
 ENDPIPROC(memcpy)

arch/arm64/lib/memmove.S

@@ -57,9 +57,8 @@ C_h	.req	x12
 D_l	.req	x13
 D_h	.req	x14
 
-	.weak memmove
 ENTRY(__memmove)
-ENTRY(memmove)
+WEAK(memmove)
 	prfm    pldl1strm, [src, #L1_CACHE_BYTES]
 	cmp	dstin, src
 	b.lo	__memcpy

arch/arm64/lib/memset.S

@@ -54,9 +54,8 @@ dst		.req	x8
 tmp3w		.req	w9
 tmp3		.req	x9
 
-	.weak memset
 ENTRY(__memset)
-ENTRY(memset)
+WEAK(memset)
 	mov	dst, dstin	/* Preserve return value.  */
 	and	A_lw, val, #255
 	orr	A_lw, A_lw, A_lw, lsl #8