* Don't try to find where $(CXX) is, just use it
* Don't muck with CXXFLAGS

--- a/Makefile
+++ b/Makefile
@@ -85,13 +85,9 @@
 # ------------------------------------
 INSTALL := $(shell which install)
 RM      := $(shell which rm) -f
-CXX     ?= g++
 SED     := $(shell which sed)
 WINDRES :=
 
-ifeq (,$(findstring /,$(CXX)))
-  CXX   := $(shell which $(CXX))
-endif
 
 
 # if this is a Windows target, prefer mingw32-g++ over g++
@@ -231,8 +227,6 @@
     CPPFLAGS := ${CPPFLAGS} -DATANKS_DEBUG_LOGTOFILE
   endif
 
-else
-  CXXFLAGS := -march=native ${CXXFLAGS} -O2
 endif