libucontext: proper patch for x86

Make renaming of local __i868.get_pc_thunk.bx to i686_get_pc_thunk_bx a proper patch.

srcpkgs/libucontext/patches/arch-x86-i668_get_thunk_bx.patch

@@ -0,0 +1,20 @@
+--- arch/x86/startcontext.S	2020-05-18 05:28:21.000000000 +0200
++++ arch/x86/startcontext.S	2021-01-02 23:52:32.728187160 +0100
+@@ -18,7 +18,7 @@
+ 	cmpl	$0, (%esp)
+ 
+ 	/* restore global offset table, exit@plt and __setcontext@plt need this */
+-	call	__i686.get_pc_thunk.bx
++	call	i686_get_pc_thunk_bx
+ 	addl	$_GLOBAL_OFFSET_TABLE_, %ebx
+ 
+ 	/* if we have no linked context, lets get out of here */
+@@ -35,7 +35,7 @@
+ 	/* something is really hosed, call hlt to force termination */
+ 	hlt
+ 
+-__i686.get_pc_thunk.bx:
++i686_get_pc_thunk_bx:
+ 	mov	(%esp), %ebx
+ 	ret
+ END(__start_context)

srcpkgs/libucontext/template

@@ -22,9 +22,6 @@ mips*)  export LIBUCONTEXT_ARCH="mips";;
 esac
 
 do_build() {
-	case "${XBPS_TARGET_MACHINE}" in
-	i686*) vsed -i arch/x86/startcontext.S -e "s;__i686.get_pc_thunk.bx;i686_get_pc_thunk_bx;g" ;;
-	esac
 	make ARCH="${LIBUCONTEXT_ARCH}"
 }