Make Toolchain::makeCommand return a full path to the make command

Requires passing in the environment to use. Also now the mingw toolchain
has a fall back to make.exe on windows. And the msvc toolchain falls
back to nmake even if the "use Jom" option is used.

Task-number: QTCREATORBUG-7831

Change-Id: I850a96da41a380eef8c6992e27a72fb63958c456
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Peter Kümmel <syntheticpp@gmx.net>