cmake's default compiler names incorrect when crosscompiling

[Michał Sawicz]

[Impact]

It is not possible to cross-build packages that use dh with cmake build system, as incorrect compiler is set for the compilation.

[Testcase]
* Create mk-sbuild chroot with a cross target, e.g. --target arm64
* Attempt to cross-build a package for arm64, which uses dh, and cmake
* observe that a crosscompiler is found and detected correctly at configure step, instead of failing to configure with a non-existant compiler

[Regression Potential]
Current cmake crossbuild is b0rked, this patch does not touch any other codepaths.

[Original bug report]
When using dh_auto_configure with cmake, the compiler names are wrong, this patch upstream fixes it:

https://anonscm.debian.org/git/debhelper/debhelper.git/patch/lib/Debian/Debhelper/Buildsystem/cmake.pm?id=61d575451f028e2bba666d40ee1dedc8c6308f40

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: debhelper 9.20160115ubuntu3
ProcVersionSignature: Ubuntu 4.13.0-16.19-generic 4.13.4
Uname: Linux 4.13.0-16-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.10
Architecture: amd64
Date: Mon Oct 30 18:01:02 2017
PackageArchitecture: all
ProcEnviron:
 TERM=screen-256color
 PATH=(custom, no user)
 LANG=C.UTF-8
SourcePackage: debhelper
UpgradeStatus: No upgrade log present (probably fresh install)