Standardize NO_CCACHE flag and ccache definitions

[Alex Dupre]

Edwin Groothuis ha scritto:
> Unfortunately /etc/make.conf is read before the ports Makefile is
> read, so this in /etc/make.conf isn't going to work anymore:
> 
> 	.if !defined(NO_CCACHE)
> 	CC=/usr/local/libexec/ccache/cc
> 	CXX=/usr/local/libexec/ccache/c++
> 	CPP=/usr/local/libexec/ccache/cpp
> 	CCACHE_DIR=/usr/local/ccache
> 	.endif

This is not the recommended way to use ccache. Look at the port's 
documentation.

-- 
Alex Dupre