Respect CFLAGS and LDFLAGS
https://bugs.gentoo.org/971364
--- a/makefile	2026-03-20 08:13:14.623645775 -0000
+++ b/makefile	2026-03-20 08:13:21.424581019 -0000
@@ -1215,7 +1215,7 @@
   BUILD_FEATURES = - debugging support
 else
   ifneq (,$(findstring clang,$(COMPILER_NAME))$(findstring LLVM,$(COMPILER_NAME)))
-    CFLAGS_O = -O2 -fno-strict-overflow
+    CFLAGS_O ?= -O2 -fno-strict-overflow
     GCC_OPTIMIZERS_CMD = ${GCC} --help
     NO_LTO = 1
   else
@@ -1223,10 +1223,10 @@
     ifeq (Darwin,$(OSTYPE))
       CFLAGS_O += -O4 -flto -fwhole-program
     else
-      CFLAGS_O := -O2
+      CFLAGS_O ?= -O2
     endif
   endif
-  LDFLAGS_O = 
+  LDFLAGS_O ?= 
   GCC_MAJOR_VERSION = $(firstword $(subst  ., ,$(GCC_VERSION)))
   ifneq (3,$(GCC_MAJOR_VERSION))
     ifeq (,$(GCC_OPTIMIZERS_CMD))