No way to specify custom C and C++ compilers in configuration

[mstewartgallus]

There doesn't seem to be a way to specify custom C and C++ compiler in configuration.
As a bonus, if this is done then the --enable-clang and --enable-ccache flags can be thrown away.

Context: I need this capability because my system build of GCC is only at 4.6 (I'm using one of those really old long term support distributions) and I want to specify my custom build of GCC 4.9 so I can build the version of LLVM packaged with Rust. Yes, I could hack around this but it's simplest if Rust gains options to override the compilers.

[pnkfelix]

I thought if you have the CC and CXX environment variables set, it will use those compilers. I haven't checked closely recently; is the problem that we only support those environment variables during make itself, and not during the execution of the configure script?

Anyway, we should try to make sure that some functionality of this sort works. (Though I don't think it would be a release blocker.)

Also, I am not sure we would be able to remove --enable-ccache if we fixed this issue. In particular we have at least one ccache specific hack to avoid spurious warnings from clang on a ccache-miss; you can review some of those details by looking at PR #6805.

[alexcrichton]

You can also modify your PATH to point to the relevant compiler. The linux snapshot bots have a system gcc of 4.6 and I installed a 4.7 toolchain on them in a nonstandard location, and they're all building with the 4.7 toolchain.

A sample of the ./configure output: http://buildbot.rust-lang.org/builders/nightly-linux/builds/53/steps/configure/logs/stdio

[mstewartgallus]

@pnkfelix, yes the CC and CXX environment variables don't work for configuring. I did not know about the reason for the --enable-ccache option, thanks.

@alexcrichton, Okay I'll use the PATH workaround for now (although that means one has to specify the PATH while doing the make as well).

[pnkfelix]

okay, so maybe one easy way to satisfy this would be to make the configure script respect the CC and CXX environment variables, if set.