Log Message:
cmake: updated to 3.12.3

Changes in 3.12.3 since 3.12.2:
* CTest: Fix --test-load regression
* FindMPI: Restore MPI__COMPILE_FLAGS as a command-line string
* FindDoxygen: Ensure policy settings allow use of IN_LIST
* libarchive: Backport fix for build with LibreSSL 2.7
* libuv: do not require PATH_MAX to be defined
* VS: Fix CSharp flag selection when linking to a static C++ library
* CSharp: Fix regression in VS project type selection
* CTest: Fix regression in ctest_start()
* Help: TESTS property: clarify usage.