Update crtbegin.c and crt*.S to support Armv8.5-A BTI

These files are linked to all ELF files therefore they must support BTI.

Test: Tested on FVP with BTI enabled using a patched clang.

Co-authored-by: Gabor Kertesz <gabor.kertesz@arm.com>
Co-authored-by: Daniel Kiss   <daniel.kiss@arm.com>
Co-authored-by: Tamas Petz    <tamas.petz@arm.com>

Change-Id: If5df0722e649bcdb8c4afb0531831dff42103c9c
diff --git a/libc/arch-common/bionic/crtend.S b/libc/arch-common/bionic/crtend.S
index 87d1120..0166428 100644
--- a/libc/arch-common/bionic/crtend.S
+++ b/libc/arch-common/bionic/crtend.S
@@ -28,6 +28,12 @@
 
 #include "asm_multiarch.h"
 
+#if defined(__aarch64__)
+#include <private/bionic_asm_arm64.h>
+
+__bionic_asm_custom_note_gnu_section()
+#endif
+
 	.section .preinit_array, "aw"
 	ASM_ALIGN_TO_PTR_SIZE
 	ASM_PTR_SIZE(0)