Only specify debug library name for msvc and intel

[jhunold]

Boost.Build can then fallback to the release libraries for these
compilers for user-defined variants.

[jzmaddock]

Can you elaborate a little on this? As far as I know, you must link to ICU binaries built using the same options as your program (ie runtime lib variant) otherwise really bad thing happen.

[jhunold]

Basically I am using my "develop" for years. This is just "release" with debug symbols enabled so I get a minimal backtrace while having fast computation and quite noisy logfiles. This setup is link-compatible with the (Boost-)libraries produces by release. Hardcoding the library names for both and prevents Boost.Build from chosing a valid alternative when encountering develop. So this patch fixes my case while not breaking the other usages. As soon as you need advanced settings (iterator_debugging etc.) this selection magic will break into much more pieces.

[jhunold]

John, do you need more information?

[jzmaddock]

John, do you need more information?

No, I just want to test it locally - and as I'm recovering from laptop
failure and don't have have the things I need installed yet it may be a
couple of days :(

Will get back to you shortly, John.

[jzmaddock]

Tested OK.