Makefile and autoconf/automake gcc version check

Makefile:

GCC_VERSION_GE_45 := $(shell g++ -dumpversion | gawk '{print $$1>=4.5?"1":"0"}')
ifeq ($(GCC_VERSION_GE_45),1)
    AM_CXXFLAGS +=-Wunreachable-code
endif

Note the use of double $ sign inside gawk script.


In Autoconf/Automake:
1. Add the following line to configure.ac
  AM_CONDITIONAL(GCC_GE_45, test `g++ -dumpversion | gawk '{print $1>=4.5?"1":"0"}'` = 1)

2. Add the following line to Makefile.am

  include $(top_srcdir)/common.mk

3. Add the following lines to common.mk

if GCC_GE_45

    AM_CXXFLAGS +=-Wunreachable-code

endif