arch: fix MIPS NaN and floating-point handling

Hello All!

Not all architectures we support have support in upstream gcc, glibc, binutils, and/or linux. In some cases, only a few specific cores do not have that support.

Furthermore, some architecture, specific cores, or core behaviour/setup (like the MIPS NaN support) got support in a specific gcc version.

Currently, we have to account for this in at least four locations:
- the architecture
- the toolchain backend choice (internal or externsal)
- the gcc version choice
- each external toolchain

This third series fixes the way we handle NaN and floating point in the MIPS case.

Currently, they both depend on the gcc version. However, this is opposite what we usually do in Buildroot: we let the user select their hardware settings, and then limit the software list according to that which suports the user's hardware.

So, now that we have a mean for architectures to specify the minimum gcc version they require, we use that to limit the gcc version depending on the NaN and FP settings the user did set.

And this concludes this three-series series (a meta-series, made up of three series. It's series all the way down! Muahaha! ;-) )

Regards,
Yann E. MORIN.

The following changes since commit 41eeac74f986790fe26f03ebf05322120d2c04da

package/gcc: slight cleanup and reorg in remaining arch depends (2017-09-03 11:14:53 +0200)

are available in the git repository at:

git://git.buildroot.org/~ymorin/git/buildroot.git

for you to fetch changes up to a191b26508b5cddafe1059f13fcd2aa4b2ebd689

toolchain/buildroot: glibc requires header >= 4.5 with NaN-2008 (2017-09-03 11:49:02 +0200)

----------------------------------------------------------------
Yann E. MORIN (3):
arch/mips: inverse the NaN logic
arch/mips: inverse the mfpxx logic toolchain/buildroot: glibc requires header >= 4.5 with NaN-2008

 arch/Config.in.mips                     | 6 +++---
 package/gcc/gcc.mk                      | 2 ++
 toolchain/toolchain-buildroot/Config.in | 1 +
 toolchain/toolchain-common.in           | 4 ----
 4 files changed, 6 insertions(+), 7 deletions(-)

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