Motivation for this change

While reviewing #75798 I've noticed a repetitive pattern of setting BUILD_SHARED_LIBS=OFF for many of the cmake builds. It makes sense to just set it for all builds.

Background

CMake has a BUILD_SHARED_LIBS option which governs the behaviour of the add_library() function in case when the library type is not specified. Its default value is "OFF" meaning default to STATIC. It is not uncommon to explicitly redefine the option:

option(BUILD_SHARED_LIBS "Build shared instead of static library" OFF)

This adds the BUILD_SHARED_LIBS option to the list of options in the CMake gui. There is a different variation of the redefinition where the default value is changed to "ON".

Some packages allow to provide both shared and static libraries. Additional custom options are defined to facilitate this. These options may or may not break the default convention for the BUILD_SHARED_LIBS.

In Nixpkgs

Here are a few data points for nixpkgs:

# grep -r -iE "\\-DBUILD_SHARED_LIBS=(ON|TRUE|1)" pkgs/ | wc -l
39
# grep -r -iE "\\-DBUILD_SHARED_LIBS=(OFF|FALSE|0)" pkgs/ | wc -l
2
# grep -r "\\-DBUILD_SHARED_LIBS" . | wc -l
46

# grep -r "\\-DBUILD_STATIC_LIBS" . | wc -l
4
# grep -r "\\-DBUILD_" . | grep SHARED | wc -l
48
# grep -r "\\-DBUILD_" . | grep STATIC | wc -l
9

This PR should help with 39 cases where we enabled building of shared libraries. It will also help in cases when the default value of the BUILD_STATIC_LIBS option was changed to "ON"

In upstream

• fmt: chose to not override BUILD_STATIC_LIBS (Please make BUILD_SHARED_LIBS a cmake option fmtlib/fmt#600).
• gtest: BUILD_STATIC_LIBS overridden with default to "OFF" https://github.com/google/googletest/blob/306f3754a71d6d1ac644681d3544d06744914228/googletest/CMakeLists.txt#L69-L71
• hyperscan: BUILD_SHARED_LIBS overridden with default to "OFF", additional option BUILD_SHARED_AND_STATIC_LIBS available https://github.com/intel/hyperscan/blob/d79973efb1fcf5ed338122882c1f896829767fb6/CMakeLists.txt#L109-L110
• pugixml: BUILD_SHARED_LIBS overridden with default to "OFF", additional option BUILD_SHARED_AND_STATIC_LIBS available
  https://github.com/zeux/pugixml/blob/41b6ff21c455865bb8ef67c5952b7f895b62bacc/CMakeLists.txt#L26-L28

Things done

fmt

# ls -1 $(nix-build . -A fmt)/lib
libfmt.so
libfmt.so.6
libfmt.so.6.0.0
# ls -1 $(nix-build . -A pkgsStatic.fmt)/lib
libfmt.a

gtest

# ls -1 $(nix-build . -A gtest)/lib
libgmock_main.so
libgmock.so
libgtest_main.so
libgtest.so
# ls -1 $(nix-build . -A pkgsStatic.gtest)/lib
libgmock.a
libgmock_main.a
libgtest.a
libgtest_main.a