emacs: Use makefile-gmake-mode in Makefile*s

Use `makefile-gmake-mode' instead of `makefile-mode' because the
former also highlights ifdef et al. while the latter does not.

"./Makefile.global" and one "Makefile.local" failed to specify any
major mode at all but doing so is necessary because Emacs does not
automatically figure out that these are Makefiles (of any flavor).

Makefile.global

@@ -1,3 +1,4 @@
+# -*- makefile-gmake -*-
 # Here's the (hopefully simple) versioning scheme.
 #
 # Releases of notmuch have a two-digit version (0.1, 0.2, etc.). We

Makefile.local

@@ -1,4 +1,4 @@
-# -*- makefile -*-
+# -*- makefile-gmake -*-
 
 .PHONY: all
 all: notmuch notmuch-shared build-man build-info ruby-bindings python-cffi-bindings

bindings/Makefile.local

@@ -1,4 +1,4 @@
-# -*- makefile -*-
+# -*- makefile-gmake -*-
 
 dir := bindings
 

compat/Makefile.local

@@ -1,4 +1,4 @@
-# -*- makefile -*-
+# -*- makefile-gmake -*-
 
 dir := compat
 extra_cflags += -I$(srcdir)/$(dir)

completion/Makefile.local

@@ -1,4 +1,4 @@
-# -*- makefile -*-
+# -*- makefile-gmake -*-
 
 dir := completion
 

doc/Makefile.local

@@ -1,4 +1,4 @@
-# -*- makefile -*-
+# -*- makefile-gmake -*-
 
 dir := doc
 

emacs/Makefile.local

@@ -1,4 +1,4 @@
-# -*- makefile -*-
+# -*- makefile-gmake -*-
 
 dir := emacs
 emacs_sources := \

lib/Makefile.local

@@ -1,4 +1,4 @@
-# -*- makefile -*-
+# -*- makefile-gmake -*-
 
 dir := lib
 

parse-time-string/Makefile.local

@@ -1,3 +1,5 @@
+# -*- makefile-gmake -*-
+
 dir := parse-time-string
 extra_cflags += -I$(srcdir)/$(dir)
 

performance-test/Makefile.local

@@ -1,4 +1,4 @@
-# -*- makefile -*-
+# -*- makefile-gmake -*-
 
 dir := performance-test
 

test/Makefile.local

@@ -1,4 +1,4 @@
-# -*- makefile -*-
+# -*- makefile-gmake -*-
 
 dir := test
 

util/Makefile.local

@@ -1,4 +1,4 @@
-# -*- makefile -*-
+# -*- makefile-gmake -*-
 
 dir := util
 extra_cflags += -I$(srcdir)/$(dir)