import GCC 5.4.0 release. there's not a lot of new info though at
least these 135 (!) GCC PRs have been fixed by the update:

68730 69714 67550 70209 71254 70839 69737 70067 67355 67172 69239
65779 69546 70272 70421 65985 67339 67411 68309 68585 68679 68890
68949 69009 70139 70494 68162 69135 70306 68965 70297 70635 66786
69098 70347 69719 70526 70941 69400 69577 69447 65689 65886 65932
66655 68269 68789 69614 69648 69666 69764 69794 70044 70052 65726
68910 64289 68671 68835 69669 70329 71204 69355 67364 68049 68998
69323 69743 69995 69146 68651 67755 67484 68790 68907 69099 69496
69509 69516 70393 69222 69703 69939 70609 71004 71005 71036 71037
71038 68636 69013 69606 70115 70333 70430 60290 70356 69305 70024
67781 69414 69140 70510 60164 66635 67896 68106 68298 68449 68779
68921 68986 69037 69147 69194 69366 69399 69705 69917 69969 70613
71317 69268 70269 69032 65702 69219 69484 65996 66680 68283 69603
70350 67451 61397

import GCC 5.3.0. see these urls for details which are too large to
include here:

http://gcc.gnu.org/gcc-4.9/changes.html
http://gcc.gnu.org/gcc-5/changes.html

(note that GCC 5.x is a release stream like GCC 4.9.x, 4.8.x, etc.)


the main issues we will have are:

The default mode for C is now -std=gnu11 instead of -std=gnu89.

ARM:
The deprecated option -mwords-little-endian has been removed.
The options -mapcs, -mapcs-frame, -mtpcs-frame and -mtpcs-leaf-frame
which are only applicable to the old ABI have been deprecated.

MIPS:
The o32 ABI has been modified and extended. The o32 64-bit
floating-point register support is now obsolete and has been removed.
It has been replaced by three ABI extensions FPXX, FP64A, and FP64.
The meaning of the -mfp64 command-line option has changed. It is now
used to enable the FP64A and FP64 ABI extensions.