Cygwin: gendef: add _sigfe_maybe for TLS initialization checks on AArch64

Signed-off-by: Thirumalai Nagalingam <thirumalai.nagalingam@multicorewareinc.com>

winsup/cygwin/scripts/gendef

@@ -367,8 +367,24 @@ EOF
 	.include "tlsoffsets"
 	.text
 
-_sigfe_maybe:
-	.global _sigbe
+	.seh_proc _sigfe_maybe
+_sigfe_maybe:					# stack is aligned on entry!
+	.seh_endprologue
+	ldr     x10, [x18, #0x8]		// Load TEB pointer in x10
+	ldr     x11, =_cygtls.initialized	// Load relative offset of _cygtls.initialized
+	add     x11, x10, x11                  	// compute absolute address and store in x11
+	cmp     sp, x11				// Compare current stack pointer with TLS location
+	b.hs    0f                             	// if sp >= tls, skip TLS logic
+	ldr     w12, [x11]                    	// Load the value at _cygtls.initialized (32-bit)
+	movz    w13, #0xc763			// Prepare magic value(0xc763173f) lower 16 bits
+	movk    w13, #0x173f, lsl #16		// Add upper 16 bits, full value now in w13
+	cmp     w12, w13			// Compare loaded value with magic
+	b.ne    0f                              // If not equal, not initialized, skip TLS logic
+	ret
+0:
+	ret
+	.seh_endproc
+
 _sigfe:
 _sigbe:
 	.global	sigdelayed