Allow compilation of the compiler with 2.6.x again on Unix systems.

compiler.pas:
	check for "FPC_VERSION>2 or FPC_RELEASE>6" before using unixcp


git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@23746 3ad0048d-3df7-0310-abae-a5850022a9f2