Updated makefile with various improvements

Makefile

@@ -4,10 +4,9 @@ obj = $(src:.c=.o)
 # Build type parameter
 
 ifeq ($(BUILD),debug)
-    CFLAGS_BUILD = -O0 -ggdb -Wall #-fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
+    CFLAGS_BUILD = -O0 -ggdb -Wall
     GLAD_GEN = c-debug
 	STRIP_CMD = $(info Skipping `strip` for debug builds)
-#    ASAN = -lasan
 else
     CFLAGS_BUILD = -O2 -Wstringop-overflow=0
     GLAD_GEN = c
@@ -25,6 +24,10 @@ ifndef INSTALL
     endif
 endif
 
+ifndef EXECDIR
+    EXECDIR = /usr/bin/
+endif
+
 # Install type parameter
 
 ifeq ($(INSTALL),standalone)
@@ -33,10 +36,12 @@ endif
 
 ifeq ($(INSTALL),unix)
     CFLAGS_INSTALL = -DGLAVA_UNIX
-    ifdef XDG_CONFIG_DIRS
-        SHADER_DIR = $(firstword $(subst :, ,$(XDG_CONFIG_DIRS)))/glava
-    else
-        SHADER_DIR = etc/xdg/glava
+    ifndef SHADERDIR
+        ifdef XDG_CONFIG_DIRS
+            SHADERDIR = /$(firstword $(subst :, ,$(XDG_CONFIG_DIRS)))/glava/
+        else
+            SHADERDIR = /etc/xdg/glava/
+        endif
     endif
 endif
 
@@ -52,7 +57,9 @@ endif
 
 ifeq ($(INSTALL),osx)
     CFLAGS_INSTALL = -DGLAVA_OSX
-    SHADER_DIR = Library/glava
+    ifndef SHADERDIR
+        SHADERDIR = /Library/glava
+    endif
 endif
 
 LDFLAGS += $(ASAN) -lpulse -lpulse-simple -pthread $(LDFLAGS_GLFW) -ldl -lm -lX11 -lXext $(LDFLAGS_GLX)
@@ -64,30 +71,38 @@ ifeq ($(GLAVA_VERSION),\"\")
     GLAVA_VERSION = \"unknown\"
 endif
 
+ifdef DESTDIR
+	DESTDIR += /
+endif
+
 GLAD_INSTALL_DIR = glad
-GLAD_SRCFILE = ./glad/src/glad.c
+GLAD_SRCFILE = glad.c
 GLAD_ARGS = --generator=$(GLAD_GEN) --extensions=GL_EXT_framebuffer_multisample,GL_EXT_texture_filter_anisotropic
-CFLAGS_COMMON = -I glad/include -DGLAVA_VERSION="$(GLAVA_VERSION)"
+CFLAGS_COMMON = -DGLAVA_VERSION="$(GLAVA_VERSION)" -DSHADER_INSTALL_PATH="\"$(SHADERDIR)\""
 CFLAGS_USE = $(CFLAGS_COMMON) $(CFLAGS_GLX) $(CFLAGS_GLFW) $(CFLAGS_BUILD) $(CFLAGS_INSTALL) $(CFLAGS)
 
 # Store relevant variables that may change depending on the environment or user input
-STATE = $(BUILD),$(INSTALL),$(ENABLE_GLFW),$(DISABLE_GLX),$(PYTHON),$(CC),$(CFLAGS_USE)
+STATE = $(BUILD),$(INSTALL),$(PREFIX),$(ENABLE_GLFW),$(DISABLE_GLX),$(PYTHON),$(CC),$(CFLAGS_USE)
 # Only update the file if the contents changed, `make` just looks at the timestamp
 $(shell if [[ ! -e build_state ]]; then touch build_state; fi)
 $(shell if [ '$(STATE)' != "`cat build_state`" ]; then echo '$(STATE)' > build_state; fi)
 
 all: glava
 
-%.o: %.c glad.o build_state
-	$(CC) $(CFLAGS_USE) -o $@ -c $(firstword $<)
+%.o: %.c build_state
+	@$(CC) $(CFLAGS_USE) -o $@ -c $(firstword $<)
+	@echo "CC $@"
 
 glava: $(obj)
-	$(CC) -o glava $(obj) glad.o $(LDFLAGS)
+	@$(CC) -o glava $(obj) $(LDFLAGS)
+	@echo "CC glava"
 	$(STRIP_CMD)
 
-glad.o: build_state
-	cd $(GLAD_INSTALL_DIR) && $(PYTHON) -m glad $(GLAD_ARGS) --out-path=.
-	$(CC) $(CFLAGS_USE) -o glad.o $(GLAD_SRCFILE) -c
+.PHONY: glad
+glad: build_state
+	@cd $(GLAD_INSTALL_DIR) && $(PYTHON) -m glad $(GLAD_ARGS) --local-files --out-path=.
+	@cp glad/*.h .
+	@cp glad/glad.c .
 
 # Empty build state goal, used to force some of the above rules to re-run if `build_state` was updated
 build_state: ;
@@ -96,14 +111,17 @@ build_state: ;
 clean:
 	rm -f $(obj) glava glad.o build_state
 
+EXECTARGET = $(shell readlink -m "$(DESTDIR)$(EXECDIR)/glava")
+SHADERTARGET = $(shell readlink -m "$(DESTDIR)$(SHADERDIR)")
+
 .PHONY: install
 install:
-	install -Dm755 glava "$(DESTDIR)/usr/bin/glava"
-	install -d "$(DESTDIR)/$(SHADER_DIR)"
-	cp -Rv shaders/* "$(DESTDIR)/$(SHADER_DIR)"
+	install -Dm755 glava $(EXECTARGET)
+	install -d $(SHADERTARGET)
+	cp -Rv shaders/* $(SHADERTARGET)
 
 .PHONY: uninstall
 uninstall:
-	rm /usr/bin/glava
-	rm -rf $(SHADER_DIR)/glava
+	rm $(EXECTARGET)
+	rm -rf $(SHADERTARGET)