Darwin: Correct a version check.

Darwin: Correct a version check.

When the version for dsymutil comes from a clang build, it is
of the form NNmm.pp.qq where NN and mm are the major and minor
LLVM version components.  We need to check for a major version
greater than or equal to 7 - so use 700 in the check.

gcc/ChangeLog:

	* config/darwin.cc (darwin_override_options): Update the
	clang major version value in the dsymutil check.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>