Regarding the actual manual, it's hard to give a clear answer.
If it is (at least partially) derived from the docinfo like Mario's manual, then very strictly speaking, it falls under the GPL as derived work, and the author must publish sources (screenshots are mostly considered not to be protected by copyright, or may be defended by fair use in some countries, unless they predominantly or exclusively consist of copyrighted original artwork).
However, I generally think that in the case of documentation, a too strict interpretation of licenses such as the GPL is a bit pedantic and unsuitable.
Documentation is meant to make everyone's life happier, it helps users to understand a program, and it is very clearly beneficial to a program's acceptance (unless it's a really bad documentation). Thus, punishing people for writing documentation in obviously good faith looks a bit silly to me.
Regarding the binaries, Dje is right. The GPL does demand that you publish the sources for both MinGW and Code::Blocks if you offer downloads (a link to the source code is not enough). But no worries, the FBI won't knock down your front door during the next 8 hours, please just add the sources when you find the time.
Unluckily, it is not possible (other than by dual-licensing) to make exceptions on the source code clause for several legal reasons (which, to make it more difficult, are different in different countries, too).
If publishing the source code is a problem (due to bandwidth, or for whatever reason), it is still easy to make everyone happy by writing something like:
Download the
MinGW installer:
MinGW-5.1.3.exe