Commit v3.0.0-rc1~111^2 (QNX: Introduce QCC compiler id for that
QNX platform compiler., 2014-01-20) split handling of the QNX QCC
compiler into a separate compiler-id.  That refactoring results in
the QCC compiler not using the CMake-compiler-id "GNU", which means
that the __compiler_gnu macro is no longer executed for it.

Add Compiler/QCC*.cmake modules to define and call the __compiler_qcc
macro and teach it to call __compiler_gnu internally.  Remove the
corresponding pieces from the Platform/QNX*.cmake modules.

It is also necessary to change the language conditional to dereference
the lang macro parameter, which is another bug introduced by the
same commit.  The extra -lang-c++ flag is only necessary when the CXX
compiler is specified as 'qcc' instead of 'QCC' in the toolchain file,
which is why this bug was not noticed before.  The flag is also necessary
in that case when linking in order to find the appropriate standard
libraries.  The flag was not previously added when linking executables,
so linking failed even with CMake 2.8.12 with the lower-case compiler-id.

Co-Author: Brad King <brad.king@kitware.com>