configure: separate simple EGL clients from others

Separate simple EGL clients from other simple clients. This allows to
build either simple-shm or simple-egl, whichever you want. We avoid
linking libEGL and GLESv2 into simple-shm, and we can build simple-shm
even if nothing provides EGL, GLESv2, or wayland-egl APIs.

Change the options in configure --help from --enable to --disable, since
these are enabled by default, and you would normally only ever give the
--disable flavor. Add descriptions.

Remove the #define BUILD_SIMPLE_CLIENTS since it is not used.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>

clients/Makefile.am

@@ -5,7 +5,8 @@ bin_PROGRAMS =					\
 noinst_PROGRAMS =				\
 	$(clients_programs)			\
 	$(poppler_programs)			\
-	$(simple_clients_programs)
+	$(simple_clients_programs)		\
+	$(simple_egl_clients_programs)
 
 libexec_PROGRAMS =				\
 	$(desktop_shell)			\
@@ -21,14 +22,9 @@ AM_CPPFLAGS =					\
 
 if BUILD_SIMPLE_CLIENTS
 simple_clients_programs =			\
-	simple-egl				\
 	simple-shm				\
 	simple-touch
 
-simple_egl_SOURCES = simple-egl.c
-simple_egl_CPPFLAGS = $(SIMPLE_CLIENT_CFLAGS)
-simple_egl_LDADD = $(SIMPLE_CLIENT_LIBS) -lm
-
 simple_shm_SOURCES = simple-shm.c 		\
 	../shared/os-compatibility.c		\
 	../shared/os-compatibility.h
@@ -42,6 +38,15 @@ simple_touch_CPPFLAGS = $(SIMPLE_CLIENT_CFLAGS)
 simple_touch_LDADD = $(SIMPLE_CLIENT_LIBS)
 endif
 
+if BUILD_SIMPLE_EGL_CLIENTS
+simple_egl_clients_programs =			\
+	simple-egl
+
+simple_egl_SOURCES = simple-egl.c
+simple_egl_CPPFLAGS = $(SIMPLE_EGL_CLIENT_CFLAGS)
+simple_egl_LDADD = $(SIMPLE_EGL_CLIENT_LIBS) -lm
+endif
+
 if BUILD_CLIENTS
 terminal = weston-terminal