mg: set -fcommon and avoid overriding step_make_install

Fixes build with ndk-r23, and avoids overriding
termux_step_make_install for no good reason.

packages/mg/GNUmakefile.patch

@@ -1,7 +1,11 @@
-diff -u -r ../mg-20180927/GNUmakefile ./GNUmakefile
---- ../mg-20180927/GNUmakefile	2018-09-27 20:00:17.000000000 +0000
-+++ ./GNUmakefile	2018-11-17 23:55:15.804955616 +0000
-@@ -11,7 +11,7 @@
+--- ./GNUmakefile.orig	2021-11-10 19:35:46.973265640 +0000
++++ ./GNUmakefile	2021-11-10 19:34:58.803308861 +0000
+@@ -7,11 +7,11 @@
+ 
+ name=		mg
+ 
+-prefix=		/usr/local
++prefix?=		/usr/local
  bindir=		$(prefix)/bin
  libdir=		$(prefix)/lib
  includedir=	$(prefix)/include

packages/mg/build.sh

@@ -3,7 +3,7 @@ TERMUX_PKG_DESCRIPTION="microscopic GNU Emacs-style editor"
 TERMUX_PKG_LICENSE="Public Domain"
 TERMUX_PKG_MAINTAINER="@termux"
 TERMUX_PKG_VERSION=20180927
-TERMUX_PKG_REVISION=2
+TERMUX_PKG_REVISION=3
 TERMUX_PKG_SRCURL=https://github.com/hboetes/mg/archive/$TERMUX_PKG_VERSION.tar.gz
 TERMUX_PKG_SHA256=fbb09729ea00fe42dcdbc96ac7fc1d2b89eac651dec49e4e7af52fad4f5788f6
 TERMUX_PKG_AUTO_UPDATE=true
@@ -12,11 +12,7 @@ TERMUX_PKG_DEPENDS="libbsd, ncurses"
 TERMUX_PKG_BUILD_IN_SRC=true
 
 termux_step_pre_configure() {
-	CFLAGS+=" $CPPFLAGS"
-}
-
-termux_step_make_install() {
-	make prefix=$TERMUX_PREFIX install
+	CFLAGS+=" $CPPFLAGS -fcommon"
 }
 
 termux_step_create_debscripts() {