crt: Implement the indirect call helper ARM64EC adjustor thunk

Calls to this are synthesized by the linker where it is used for calling
into import libraries, this is referred to as an 'Adjustor Thunk' in
ARM64EC documentation.

Signed-off-by: Jacek Caban <jacek@codeweavers.com>

mingw-w64-crt/crt/chpe.S

diff --git a/mingw-w64-crt/crt/chpe.S b/mingw-w64-crt/crt/chpe.S
index 8311da1..20d9622 100644
--- a/mingw-w64-crt/crt/chpe.S
+++ b/mingw-w64-crt/crt/chpe.S
@@ -83,3 +83,26 @@
 	.rva  __os_arm64x_helper6
 	.rva  __os_arm64x_helper7
 	.rva  __os_arm64x_helper8
+
+/*
+ * Calls to this are synthesized by the linker when calling into import libraries,
+ * this is referred to as an 'Adjustor Thunk' in ARM64EC documentation.
+*/
+        .text
+        .balign 16
+EXPORT_SYM(__icall_helper_arm64ec)
+	.seh_proc "__icall_helper_arm64ec"
+	 stp	fp, lr, [sp, #-16]!
+	.seh_save_fplr_x 16
+	mov	fp, sp
+	.seh_set_fp
+	.seh_endprologue
+	adrp	x16, __os_arm64x_check_icall
+	ldr	x16, [x16, #:lo12:__os_arm64x_check_icall]
+	blr	x16
+	.seh_startepilogue
+	ldp	fp, lr, [sp], #16
+	.seh_save_fplr_x 16
+	.seh_endepilogue
+	br	x11
+	.seh_endproc