Make comparison of installed files case-insensitive

[vicroms]

Fixes the check that prevents two ports from installing a file with the same name by making the comparison case insensitive.

[BillyONeal]

We don't care about VS2015 so you can delete this if you want. Not worth resetting testing if that's the only change.

[BillyONeal]

Please format-manifest these.

[dg0yt]

This change leads to a CI regression in https://dev.azure.com/vcpkg/public/_build/results?buildId=107274&view=results:

• Android builds are on Linux with a case-sensitive filesystem.
• tmx installs tmx.h
• tmxparser installs Tmx.h.
• CI now reports

 error: The following files are already installed in /mnt/vcpkg-ci/installed/arm64-android and are in conflict with tmxparser:arm64-android
 Installed by tmx:arm64-android  
 include/tmx.h

[dg0yt]

The CI run for the tool update, https://dev.azure.com/vcpkg/public/_build/results?buildId=107231&view=results, had a warning only:

warning: File /Users/vcpkg/Data/installed/arm64-osx/include/Tmx.h was already present and will be overwritten

[BillyONeal]

@dg0yt I don't believe this is a regression, I believe this was broken before and we are finally detecting that it is broken.

[dg0yt]

Last vcpkg.ci run now, https://dev.azure.com/vcpkg/public/_build/results?buildId=107290

x64-android, case-sensitive filesystem: No error.

x64-osx, case-insensitive filesystem: warning

warning: File /Users/vcpkg/Data/installed/arm64-osx/include/Tmx.h was already present and will be overwritten

But there is the error in that vcpkg.pr run. Only for two in three android triplets.!?

[dg0yt]

Hm, this PR here claims to "Make comparison of installed files case-insensitive" but actually changes "case_insensitive_ascii_less", not "case_insensitive_ascii_equals".

The particular case of interest has this input set (order undefined):

include/tmx.h
include/Tmx.h.in
include/Tmx.h

[dg0yt]

vcpkg.pr https://dev.azure.com/vcpkg/public/_build/results?buildId=107523 Errors:

influxdb-cxx:x64-osx:/include/Proxy.h
libproxy:x64-osx:/include/proxy.h

coin-or-cgl:x64-osx:/lib/libCgl.a
games101-cgl:x64-osx:/lib/libCGL.a
# (Debug variant differs by to 'd` suffix.)

All ports were built from source, due to the CMake update (?) and touching the baseline.

vcpkg.ci https://dev.azure.com/vcpkg/public/_build/results?buildId=107290 Only warnings about overwriting.