make: Fixing default build flags for various OS's in makefiles

Signed-off-by: Tyler Erickson <tyler.erickson@seagate.com>

Author: vonericsen

Make/compiler-flags.mk

@@ -123,15 +123,20 @@ endif
 NEWER_WARNINGS := $(foreach flag,$(NEWER_WARNING_CANDIDATES),$(if $(call cc_supports,$(flag)),$(flag)))
 
 #===============================================================================
-# Conversion Warnings (commonly supported)
+# Conversion Warnings (test for support, some require newer compilers)
 #===============================================================================
 
+# Always available conversion warnings
 CONVERSION_WARNING_FLAGS := \
     -Wint-conversion \
-    -Wenum-conversion \
     -Wfloat-conversion \
     -Wint-to-pointer-cast
 
+# Test for -Wenum-conversion (GCC 10+, Clang 3.2+)
+ifeq ($(call cc_supports,-Wenum-conversion),yes)
+    CONVERSION_WARNING_FLAGS += -Wenum-conversion
+endif
+
 # GCC 10+ specific: -Wsign-conversion (very noisy, use while debugging)
 # NOTE: Intentionally not enabled by default per meson.build comments
 # Uncomment if desired:
@@ -243,14 +248,18 @@ endif
 # Combined CFLAGS and CXXFLAGS
 #===============================================================================
 
-# Initialize if not already set
+# Initialize if not already set (allows user to provide CFLAGS/CXXFLAGS from environment)
 CFLAGS ?=
 CXXFLAGS ?=
+LDFLAGS ?=
 
-# Combine all flags
+# Prepend our flags (our flags first, then user flags - this allows user to override)
+# Use := for one-time expansion to avoid recursive evaluation issues
 CFLAGS := $(WARNING_FLAGS) $(OPT_FLAGS) $(DEBUG_FLAGS) $(CFLAGS)
 CXXFLAGS := $(WARNING_FLAGS) $(OPT_FLAGS) $(DEBUG_FLAGS) $(CXXFLAGS)
 
+# Note: LDFLAGS is only initialized here, actual flags are added in security-hardening.mk and other files
+
 #===============================================================================
 # Save Tested Flags to Cache (for debugging)
 #===============================================================================

Make/config.mk

@@ -177,22 +177,23 @@ ifeq ($(filter $(BUILD_TYPE),$(VALID_BUILD_TYPES)),)
 endif
 
 # Optimization and debug flags based on build type
+# Use ?= so downstream packagers can override (e.g., OPTIMIZATION_FLAGS="-O2" make)
 ifeq ($(BUILD_TYPE),debug)
     # No optimization, maximum debug information
-    OPTIMIZATION_FLAGS := -O0 -g3
-    BUILD_DEFINES := -DDEBUG -D_DEBUG
+    OPTIMIZATION_FLAGS ?= -O0 -g3
+    BUILD_DEFINES ?= -DDEBUG -D_DEBUG
 else ifeq ($(BUILD_TYPE),release)
     # Full optimization, no debug info
-    OPTIMIZATION_FLAGS := -O3
-    BUILD_DEFINES := -DNDEBUG -DRELEASE
+    OPTIMIZATION_FLAGS ?= -O3
+    BUILD_DEFINES ?= -DNDEBUG -DRELEASE
 else ifeq ($(BUILD_TYPE),relwithdebinfo)
     # Optimized with debug symbols (for production debugging/profiling)
-    OPTIMIZATION_FLAGS := -O2 -g
-    BUILD_DEFINES := -DNDEBUG
+    OPTIMIZATION_FLAGS ?= -O2 -g
+    BUILD_DEFINES ?= -DNDEBUG
 else ifeq ($(BUILD_TYPE),minsize)
     # Optimize for binary size
-    OPTIMIZATION_FLAGS := -Os
-    BUILD_DEFINES := -DNDEBUG
+    OPTIMIZATION_FLAGS ?= -Os
+    BUILD_DEFINES ?= -DNDEBUG
 endif
 
 # Legacy support for static builds (deprecated, use IS_STATIC variable instead)
@@ -255,11 +256,11 @@ $(OBJ_DIR) $(LIB_DIR) $(BIN_DIR) $(OBJ_DIRS):
 #===============================================================================
 
 # Compiler and tools
-# Note: Make has a built-in default CC=cc, so we override it
-ifeq ($(CC),cc)
-    CC := gcc
-endif
-CXX ?= g++
+# Auto-detect system default compiler (cc points to gcc or clang depending on system)
+# FreeBSD/OpenBSD use clang by default, most Linux use gcc
+# Only override if CC is unset (not if it's already set to 'cc')
+CC ?= cc
+CXX ?= c++
 AR ?= ar
 STRIP ?= strip
 INSTALL ?= install