Q:

'glib.h' file not found on Max OSX 10.9

I'm trying to compile msg2pdf which is a tool to convert messages in mu4e (mu for Emacs) to pdf.
I'm receiving the following error :
/Applications/Xcode.app/Contents/Developer/usr/bin/make  all-recursive
Making all in .
  CC       msg2pdf.o
In file included from msg2pdf.c:20:
In file included from ../../lib/mu-msg.h:24:
../../lib/mu-flags.h:24:10: fatal error: 'glib.h' file not found
#include <glib.h>
         ^
1 error generated.
make[2]: *** [msg2pdf.o] Error 1
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2

Oddly, I checked the Makefile and GLIB_CFLAGS seem to be pointing on the right folder (where brew installed it). 
In fact, glib.h is located in /usr/local/Cellar/glib/2.40.0_1/include/glib-2.0.
GLIB_CFLAGS = -D_REENTRANT -I/usr/local/Cellar/glib/2.40.0_1/include/glib-2.0 -I/usr/local/Cellar/glib/2.40.0_1/lib/glib-2.0/include -I/usr/local/opt/gettext/include 
GLIB_LIBS = -L/usr/local/Cellar/glib/2.40.0_1/lib -L/usr/local/opt/gettext/lib -lgio-2.0 -lgobject-2.0 -lglib-2.0 -lintl 

How can I succeed compiling the file? Is there any command line "hack" I can use while calling 
make?
Edit
Here are the files in the directory
https://github.com/flexdec/temp
Edit 2
This is the output when using make V=1
/Applications/Xcode.app/Contents/Developer/usr/bin/make  all-recursive
Making all in .
gcc -DHAVE_CONFIG_H -I. -I../..  -I../../lib   -DICONDIR='""'  -Wall -Wextra -Wno-unused-parameter -Wdeclaration-after-statement -g -O2 -MT msg2pdf.o -MD -MP -MF .deps/msg2pdf.Tpo -c -o msg2pdf.o msg2pdf.c
In file included from msg2pdf.c:20:
In file included from ../../lib/mu-msg.h:24:
../../lib/mu-flags.h:24:10: fatal error: 'glib.h' file not found
#include <glib.h>
         ^
1 error generated.
make[2]: *** [msg2pdf.o] Error 1
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2

Edit 3
The new error I get using make V=1 now that GLIB_CFLAGS issue is fixed
/Applications/Xcode.app/Contents/Developer/usr/bin/make  all-recursive
Making all in .
gcc -DHAVE_CONFIG_H -I. -I../..  -I../../lib   -D_REENTRANT -I/usr/local/Cellar/glib/2.40.0_1/include/glib-2.0 -I/usr/local/Cellar/glib/2.40.0_1/lib/glib-2.0/include -I/usr/local/opt/gettext/include  -DICONDIR='""'  -Wall -Wextra -Wno-unused-parameter -Wdeclaration-after-statement -g -O2 -MT msg2pdf.o -MD -MP -MF .deps/msg2pdf.Tpo -c -o msg2pdf.o msg2pdf.c
msg2pdf.c:24:10: fatal error: 'gtk/gtk.h' file not found
#include <gtk/gtk.h>
         ^
1 error generated.
make[2]: *** [msg2pdf.o] Error 1
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2

A:

make V=1 instead of make will tell you what the C compiler command looks like (instead of just "CC       msg2pdf.o")—check that and make sure it includes the flags you need.
Based on a quick look at your Makefile.am, you are including $(GTK_CFLAGS) and $(WEBKIT_CFLAGS) in your AM_CPPFLAGS but not $(GLIB_CFLAGS).

