Use GNUInstallDirs instead of hard-coded path.

[ghost]

GNUInstallDirs defines several CMake variables for common FHS paths. For example, CMAKE_INSTALL_LIBDIR will expand to either lib or lib64 depending on the platform. In practice, this Fedora spec patches it out:

sed -i 's@lib/@%{_libdir}/@g' CMakeLists.txt

so this change will make that patch no longer necessary.

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Pull request checklist

Read the Contribution Guidelines for detailed information.

• Changes are described in the pull request, or an existing issue is referenced.
• The test suite compiles and runs without error.
• Code coverage is 100%. Test cases can be added by editing the test suite.
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Please don't

• The C++11 support varies between different compilers and versions. Please note the list of supported compilers. Some compilers like GCC 4.7 (and earlier), Clang 3.3 (and earlier), or Microsoft Visual Studio 13.0 and earlier are known not to work due to missing or incomplete C++11 support. Please refrain from proposing changes that work around these compiler's limitations with #ifdefs or other means.
• Specifically, I am aware of compilation problems with Microsoft Visual Studio (there even is an issue label for these kind of bugs). I understand that even in 2016, complete C++11 support isn't there yet. But please also understand that I do not want to drop features or uglify the code just to make Microsoft's sub-standard compiler happy. The past has shown that there are ways to express the functionality such that the code compiles with the most recent MSVC - unfortunately, this is not the main objective of the project.
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[coveralls]

Coverage remained the same at 100.0% when pulling 3184e9b on remyabel:gnuinstalldirs into cf8251e on nlohmann:develop.

[nlohmann]

Looks good to me.

[nlohmann]

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🔖 Release item

This issue/PR will be part of the next release of the library. This template helps preparing the release notes.

Type

• ✨ New Feature
• 🐛 Bug Fix
• ⚡️ Improvement
• 🔨 Further Change
• 🔥 Deprecated function

Description

• Use GNUInstallDirs to set library install directories. Use GNUInstallDirs instead of hard-coded path. #1673

Contributor entry

• remyabel added GNUInstallDirs to the CMake files.

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[nlohmann]

Thanks a lot!