Define SOURCES instead of OBJS in Makefiles.

OBJS is still deduced from SOURCES, but this change gives better control
over where the object files get actually written.

examples/opengl2_example/Makefile

@@ -15,8 +15,9 @@
 #CXX = clang++
 
 EXE = opengl2_example
-OBJS = main.o imgui_impl_glfw_gl2.o
-OBJS += ../../imgui.o ../../imgui_demo.o ../../imgui_draw.o
+SOURCES = main.cpp imgui_impl_glfw_gl2.cpp
+SOURCES += ../../imgui.cpp ../../imgui_demo.cpp ../../imgui_draw.cpp
+OBJS = $(addsuffix .o, $(basename $(SOURCES)))
 
 UNAME_S := $(shell uname -s)
 

examples/opengl3_example/Makefile

@@ -15,9 +15,10 @@
 #CXX = clang++
 
 EXE = opengl3_example
-OBJS = main.o imgui_impl_glfw_gl3.o
-OBJS += ../../imgui.o ../../imgui_demo.o ../../imgui_draw.o
-OBJS += ../libs/gl3w/GL/gl3w.o
+SOURCES = main.cpp imgui_impl_glfw_gl3.cpp
+SOURCES += ../../imgui.cpp ../../imgui_demo.cpp ../../imgui_draw.cpp
+SOURCES += ../libs/gl3w/GL/gl3w.c
+OBJS = $(addsuffix .o, $(basename $(SOURCES)))
 
 UNAME_S := $(shell uname -s)