Improve handling of variables set in the make environment

removes duplication on the commandline for example in a profile-build

closes https://github.com/official-stockfish/Stockfish/pull/3859

No functional change

diff --git a/src/Makefile b/src/Makefile
index cc9b4201555d4fefb3125c7b6d44ee7855d2d459..ff2452d6ad50967326580b41b75b21c7a6a8b0eb 100644 (file)
--- a/src/Makefile
+++ b/src/Makefile
@@ -345,9 +345,15 @@ endif
 ### ==========================================================================
 
 ### 3.1 Selecting compiler (default = gcc)
-CXXFLAGS += -Wall -Wcast-qual -fno-exceptions -std=c++17 $(EXTRACXXFLAGS)
-DEPENDFLAGS += -std=c++17
-LDFLAGS += $(EXTRALDFLAGS)
+ifeq ($(MAKELEVEL),0)
+       export ENV_CXXFLAGS := $(CXXFLAGS)
+       export ENV_DEPENDFLAGS := $(DEPENDFLAGS)
+       export ENV_LDFLAGS := $(LDFLAGS)
+endif
+
+CXXFLAGS = $(ENV_CXXFLAGS) -Wall -Wcast-qual -fno-exceptions -std=c++17 $(EXTRACXXFLAGS)
+DEPENDFLAGS = $(ENV_DEPENDFLAGS) -std=c++17
+LDFLAGS = $(ENV_LDFLAGS) $(EXTRALDFLAGS)
 
 ifeq ($(COMP),)
        COMP=gcc