build: install glslang-config.cmake to libdir

[Tachi107]

As glslang ships architecture dependant files, the Config file should be installed to libdir, not datadir. See #2989 (comment) for more details.

Here's the diff between the install tree before and after this patch:

$ diff <(tree install-datadir) <(tree install)
1c1
< install-datadir
---
> install
74,99c74,98
<         ├── lib
<         │   ├── cmake
<         │   │   ├── glslang-default-resource-limitsTargets.cmake
<         │   │   ├── glslangTargets.cmake
<         │   │   ├── glslangValidatorTargets.cmake
<         │   │   ├── HLSLTargets.cmake
<         │   │   ├── OGLCompilerTargets.cmake
<         │   │   ├── OSDependentTargets.cmake
<         │   │   ├── spirv-remapTargets.cmake
<         │   │   ├── SPIRVTargets.cmake
<         │   │   └── SPVRemapperTargets.cmake
<         │   ├── libGenericCodeGen.a
<         │   ├── libglslang.a
<         │   ├── libglslang-default-resource-limits.a
<         │   ├── libHLSL.a
<         │   ├── libMachineIndependent.a
<         │   ├── libOGLCompiler.a
<         │   ├── libOSDependent.a
<         │   ├── libSPIRV.a
<         │   └── libSPVRemapper.a
<         └── share
<             └── glslang
<                 ├── glslang-config.cmake
<                 ├── glslang-config-version.cmake
<                 ├── glslang-targets.cmake
<                 └── glslang-targets-debug.cmake
---
>         └── lib
>             ├── cmake
>             │   ├── glslang-default-resource-limitsTargets.cmake
>             │   ├── glslangTargets.cmake
>             │   ├── glslangValidatorTargets.cmake
>             │   ├── HLSLTargets.cmake
>             │   ├── OGLCompilerTargets.cmake
>             │   ├── OSDependentTargets.cmake
>             │   ├── spirv-remapTargets.cmake
>             │   ├── SPIRVTargets.cmake
>             │   └── SPVRemapperTargets.cmake
>             ├── glslang
>             │   ├── glslang-config.cmake
>             │   ├── glslang-config-version.cmake
>             │   ├── glslang-targets.cmake
>             │   └── glslang-targets-debug.cmake
>             ├── libGenericCodeGen.a
>             ├── libglslang.a
>             ├── libglslang-default-resource-limits.a
>             ├── libHLSL.a
>             ├── libMachineIndependent.a
>             ├── libOGLCompiler.a
>             ├── libOSDependent.a
>             ├── libSPIRV.a
>             └── libSPVRemapper.a
101c100
< 15 directories, 83 files
---
> 14 directories, 83 files

[CLAassistant]

All committers have signed the CLA.

[theblackunknown]

I was re-reading CMake find_package Config Mode Search Procedure page, and was wondering if we could use a more precise path to stress the arch dependent facet that you were looking for.

Something like <prefix>/lib/<arch>/<name>*/ seems to make sense on both Windows and Unix conventions according to the docs, what do you think ?

For convenience, copied here are all supported path patterns listed on CMake documentation page.

<prefix>/                                                       (W)
<prefix>/(cmake|CMake)/                                         (W)
<prefix>/<name>*/                                               (W)
<prefix>/<name>*/(cmake|CMake)/                                 (W)
<prefix>/(lib/<arch>|lib*|share)/cmake/<name>*/                 (U)
<prefix>/(lib/<arch>|lib*|share)/<name>*/                       (U)
<prefix>/(lib/<arch>|lib*|share)/<name>*/(cmake|CMake)/         (U)
<prefix>/<name>*/(lib/<arch>|lib*|share)/cmake/<name>*/         (W/U)
<prefix>/<name>*/(lib/<arch>|lib*|share)/<name>*/               (W/U)
<prefix>/<name>*/(lib/<arch>|lib*|share)/<name>*/(cmake|CMake)/ (W/U)

[Tachi107]

This is not needed, as it is already handled by distributions and CMake automatically. On Debian, for example, when <prefix> is /usr, CMAKE_INSTALL_LIBDIR is lib/arch-triplet, e.g. lib/x86_64-linux-gnu.

[Tachi107]

Different distros do this differently. Debian as Ubuntu use lib/arch-triplet, while others use lib, lib32, and lib64. This is always handled automatically when it matters, and upstreams should generally not care about it :)

[theblackunknown]

Perfect then ! Looks much more straightforward than what I thought !

[jeremy-lunarg]

This looks good to me. Thanks for contributions @Tachi107 and @theblackunknown!