EDIT: Stable GCC 7.1.0 is already released - see my reply below for details!
If you're very impatient waiting for the full GCC 7.1.0 release (expected this month), there's absolutely no need to wait any longer (; You can try experimental GCC 7 version with your LPC (or Kinetis) microcontroller right now (;
$ arm-none-eabi-gcc --version
arm-none-eabi-gcc (bleeding-edge-toolchain) 7.0.1 20170402 (experimental)
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
GitHub - FreddieChopin/bleeding-edge-toolchain at gcc-7-experimental
The script is able to produce a working toolchain for Linux. It is also possible to cross-compile a toolchain for Windows (32-bit or 64-bit) - either in Linux or in "Bash on Ubuntu on Windows" (I've heard it can be done, but the process is painfully slow - who would expect that? (; ).
I've tested that toolchain briefly and it appears to work fine (;