Add support for `buildcache`

[agarny]

Fixes #959.

[nickerso]

I don't know how to test this with Visual Studio. I have buildcache and point CMake at it and I can configure fine, but I'm not seeing any obvious change in the visual studio solution or the build time. I can confirm it doesn't break things, but would be good if there was something obvious I'm missing that would tell me this is having the desire impact on build times...

[agarny]

Normally, all you need is for buildcache to be on your PATH. From there, libCellML's build system should pick it up and make use of it.

Having said this, I have just checked on Windows and it's not taking advantage of buildcache (while it does on Linux and macOS). I know (or, rather, I believe since I am now doubting myself!) that I got it to work with libOpenCOR, so I tried buildcache there and... it's not working either...!?

Ok, will need to look into it in more details... Argh!

[agarny]

I had a quick look and everything works fine when building libCellML in release mode:

• Without buildcache: ~90s
• With buildcache:
  • Cold: ~105s
  • Warm: ~15s

When it comes to debug mode, I believe this is due to CMake using the /Zi option (i.e. "enable debugging information") for MSVC by default. I remember having the same issue with OpenCOR when trying to use clcache. In the end, I had to replace the /Zi option with the /Z7 option (i.e. "enable old-style debug info") to be able to take advantage of clcache. Will look into this tomorrow, but that would also explain why things didn't work for libOpenCOR either...

[agarny]

FWIW, to build libCellML with buildcache now works fine... from the command line, but... not using a Visual Studio solution.

REM Initialise VS2017's environment
call "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvars64.bat"

REM Reset buildcache for a cold build
buildcache -C
buildcache -s

REM Or... reset buildcache for a warm build
buildcache -z

REM Configure libCellML
cd [libCellML]
mkdir build
cd build
cmake -G Ninja -DLIBXML2_LIBRARY="C:\Program Files\LibXml2 2.9.6\lib\xml2.lib" ..

REM Build libCellML
ninja

REM Confirm that buildcache has properly cached our libCellML build
buildcache -s

Well, Windows/MSVC is always going to be a real PITA, so as far as I am concerned, I am happy with "just" buildcache working from the command line. IOW, this is ready for re-review.

[agarny]

not really going to be able to test this one if it isn't usable in visual studio...

I have updated my previous comment which should allow you to test things from the command line.

[nickerso]

not really going to be able to test this one if it isn't usable in visual studio...

I have updated my previous comment which should allow you to test things from the command line.

@nickerso hasn't compiled anything from a command line for a long time...