Explicit toolchain config

Hi.

I'm working on Cygwin on WIndows for TopCoder. In my environment, the following toolchains are found by a loop at https://github.com/fornwall/eclipsecoder-cpp/blob/master/src/net/fornwall/eclipsecoder/ccsupport/CCLanguageSupport.java#L58 

- Cross GCC: [cdt.managedbuild.toolchain.gnu.cross.exe.debug] 
[cdt.managedbuild.config.gnu.cross.exe.debug]
- Cygwin GCC: [cdt.managedbuild.toolchain.gnu.cygwin.exe.debug] [cdt.managedbuild.config.gnu.cygwin.exe.debug]
- XL C/C++ Tool Chain: [cdt.managedbuild.toolchain.xlc.exe.debug] [cdt.managedbuild.config.xlc.exe.debug]
- XL UPC Tool Chain: [cdt.managedbuild.toolchain.xlupc.exe.debug] [cdt.managedbuild.config.xlupc.exe.debug]
- Microsoft Visual C++: [org.eclipse.cdt.msvc.toolchain.exe.debug] [org.eclipse.cdt.msvc.exe.debug]

What toolchain is finally selected depends on the order of the enumeration and it seems to vary on environments. For example, Cross GCC is selected on my working environment while MSVC is selected on plug-in debug environment. Both of them are not my preference.

So, I added explicit configuration of toolchain in preference.

NOTE that I'm a newbie for Java and Eclipse plugin. I'm afraid it might be better to check my modifications than pull-req by others...

Thanks.