meson: update to 0.45

[InuSasha]

• generate cross-file per package, needed since Fix cross environment pollution. mesonbuild/meson#1807 was merged. build-flags can used like in cmake and configure, now.

[MilhouseVH]

1. Wouldn't an absolute path for MESON_CONF be better, eg. export MESON_CONF=$TOOLCHAIN/etc/meson-$TARGET_NAME.conf, otherwise you're creating $MESON_CONF inside the build directory of the package (although that wouldn't be guaranteed, for instance if a cd is performed in pre_configure_$TARGET you could be anywhere in the file system before "meson.conf" is created).

2. Wouldn't target specific conf files be more robust, ie. .../meson-$TARGET_NAME.conf and .../meson-$HOST_NAME.conf, as before? And we'd only need two of them?

3. Shouldn't we only create these conf files when they don't exist? This is creating the file every time, maybe because the conf is now in the package build dir (initial rebranding to LibreELEC #1), and is no longer target specific (stripping changes #2)?

I have no objection to the function being added, but I'm not entirely comfortable with the relative path for MESON_CONF, and creating the file every time seems unnecessary when the per-target conf worked fine (is there an advantage to writing it every time?)

[InuSasha]

@MilhouseVH

1. we can make the path to cross-file absolute, but i would make it in ./scripts/build. because, i am not sure, if all needed variables are defined in setup_toolchain (PKG_BUILD, TARGET_NAME etc). And in the build script, we have a part a case which calculate the specific build path.

2. the meson is located in the build path (eg. $PKG_BUILD/.$TARGET_NAME), so a additional TARGET_NAME is not needed.

3. with the location in the build path, the cross-file is cleaned with every package clean up. and it is only generated, when the specific build step is executed. so in the most cases it had to generated, anyway. A slow down of the build process is not taken, but we always have a clean cross-file.

[MilhouseVH]

OK, then my only real concern is the relative path, as I think it should be absolute - I don't care where, so long as it's absolute. :)

If necessary, don't set export MESON_CONF in setup_toolchain as that seems unnecessary, but set it in create_meson_conf, to an absolute value, and then you should have PKG_BUILD etc.

[InuSasha]

squashed commit and clean build is done (RPi2)

[MilhouseVH]

One final suggestion - have you thought about using a Here document for https://github.com/InuSasha/LibreELEC.tv/blob/d38cadaf8c08c497189d9878fa93ed7e1a5c81f5/config/functions#L160-L177 ?

The following patch converts it into a Here document: http://ix.io/11BI (I've tested it, and it produces identical output to the individual echo "" statements).

[InuSasha]

@MilhouseVH we can change this. I like this solution more, too.
But actual, i am on a training, till eastern.

[MilhouseVH]

Ok, I can merge this and push the Here doc change in a separate PR.