"Beautify" the two-pass RCC execution

Use newlines in the Makefile for multiple commands.

Change-Id: If03617343ccf7e525ffdc27ad9df55718c63d77f
Reviewed-by: hjk <hjk121@nokiamail.com>
Add support for CONFIG += c++14

Most compilers out in the wild still don't support the flag, so we need
to compare the version number anyway. This also makes it ready for
whenever compilers start supporting -std=c++14, something we should fix
for C++11 too.

It overrides the CXX11 variable for two reasons:
 1) we reuse the mechanics in c++11.prf
 2) we avoid c++11.prf overriding the flag if qmake decides to process
    it later (CONFIG += c++14 is additive)

Change-Id: I79b6523fd9017483f2474634d1c09f2fd5ea039d
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>