autotools: fix compiling/linking gl engines on OSX.

Summary:
Until now, it was necessary to set global LDFLAGS and CFLAGS to allow
compiling (and linking) engines using OpenGL.
gl_generic used to complained about missing headers or unkown libraries.
A problem on OSX is that there is CGL (Apple's Core OpenGL) on which the whole system
relies on and GLX, when X11 is installed; and they cohabit together.
When gl_cocoa is enabled, gl_generic is now linked against CGL.
When it is not, gl_generic is compiled with and linked against GLX as a fallback.

@fix

Test Plan:
With --enable-cocoa: software_x11, opengl_x11 and opengl_cocoa are working as expected.
With --disable-cocoa: software_x11 and opengl_x11 are also working as expected.
No compiling nor linking problems have been issued.

Reviewers: cedric, raster, raoulh

Subscribers: cedric

Differential Revision: https://phab.enlightenment.org/D1723

Signed-off-by: Cedric BAIL <cedric@osg.samsung.com>

configure.ac

@@ -1805,6 +1805,28 @@ else
    evas_engine_gl_common_libs="-lGL"
 fi
 
+# The lines below fix compiling/linking of gl_generic on OSX
+if test "x${have_darwin}" = "xyes"; then
+   if test "x${have_evas_engine_gl_cocoa}" = "xyes"; then
+      # If gl_cocoa is enabled, Apple's Core OpenGL (CGL) should be the default OpenGL.
+      # CFLAGS and LIBS are determined by evas-gl_cocoa.
+      evas_engine_gl_common_libs="${evas_engine_gl_cocoa_libs}"
+      evas_engine_gl_common_cflags="${evas_engine_gl_cocoa_cflags}"
+   else
+      # If evas-gl_cocoa is disabled, the only supported OpenGL engine on OSX (for now)
+      # is evas-gl_x11. Without its CFLAGS and LIBS explicitely set, gl_generic
+      # cannot compile (nor link).
+      evas_engine_gl_common_libs=""
+      evas_engine_gl_common_cflags=""
+
+      if test "x${have_evas_engine_gl_xlib}" = "xyes"; then
+         evas_engine_gl_common_libs="${evas_engine_gl_xlib_libs}"
+         evas_engine_gl_common_cflags="${evas_engine_gl_xlib_cflags}"
+      fi
+      ### XXX Check for other supported engines supported on OSX (dec. 2014: NONE)
+   fi
+fi
+
 AC_SUBST([evas_engine_gl_common_cflags])
 AC_SUBST([evas_engine_gl_common_libs])
 

src/Makefile_Evas.am

@@ -711,6 +711,7 @@ modules_evas_engines_gl_generic_module_la_CFLAGS = \
 -I$(top_srcdir)/src/lib/evas/include \
 -I$(top_srcdir)/src/lib/evas/cserve2 \
 -I$(top_srcdir)/src/modules/evas/engines/gl_common \
+@evas_engine_gl_common_cflags@ \
 @EVAS_CFLAGS@
 modules_evas_engines_gl_generic_module_la_LIBADD = \
 modules/evas/engines/gl_common/libevas_engine_gl_common.la \