tools/cmake: Update to 3.15.1

tools/cmake: Update to 3.15.1

Update CMake to 3.15.1
Refresh patches
Remove inofficial fossies.org and replace with GitHub (link on official site)
Remove 150-C-feature-checks-Match-warnings-more-strictly.patch as it's
a no longer needed backport from upstream.
Disable ccache if GCC is 4.8, 4.9 or 5.X to avoid build failures.
Reference: https://github.com/openwrt/openwrt/pull/1929

Signed-off-by: Daniel Engberg <daniel.engberg.lists@pyret.net>
(cherry picked from commit 413c68d120043cd8ff1f4aa057d33c140bfc6bfa)