Update Makefile.in

General Flags: Flags that are always needed, such as warnings (-w) and directory inclusion (-J.), are added outside of the conditionals.
Debug Flags:
For DMD: When debugging is enabled (DEBUG=yes), the -debug flag for including debug code and -gs for generating standalone debug symbols are added.
For LDC or other compilers: -d-debug for debugging and -gc for generating debugging information are added similarly when debugging is enabled.
Optimization Flag:
The -O flag is only added when debugging is not enabled. This ensures that the program is compiled with optimizations only when it is not in debug mode.

Makefile.in

@@ -34,13 +34,18 @@ DEBUG = @DEBUG@
 DC = @DC@
 DC_TYPE = @DC_TYPE@
 DCFLAGS = @DCFLAGS@
-DCFLAGS += -w -g -O -J.
+DCFLAGS += -w -J.
 ifeq ($(DEBUG),yes)
 ifeq ($(DC_TYPE),dmd)
-DCFLAGS += -debug -gs
+# Add DMD Debugging Flags
+DCFLAGS += -g -debug -gs
 else
-DCFLAGS += -d-debug -gc
+# Add LDC Debuggging Flags
+DCFLAGS += -g -d-debug -gc
 endif
+else
+# Only add optimisation flags if debugging is not enabled
+DCFLAGS += -O
 endif
 
 ifeq ($(NOTIFICATIONS),yes)