Make configure.exe only detect each compiler once

Make configure.exe only detect each compiler once

After commit e0acf6504356f14a6352b16ffed7b59453914863, configure.exe
built with the x64 compiler could detect the same compiler twice,
breaking the -platform detection even when only one compiler is in the
path. Fix this by taking advantage of the CompilerInfo struct ordering
and ignore detection of the same compiler.

Change-Id: I583230520d2e0859196f9d7c8af31adbb981a6ca
Reviewed-by: Joerg Bornemann <joerg.bornemann@nokia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>