`PCRE2_STATIC_RUNTIME` no longer works

[HertzDevil]

CMakeLists.txt currently replaces the CMAKE_<LANG>_FLAGS_<CONFIG> variables directly in order to select a suitable MSVC runtime library:

pcre2/CMakeLists.txt

Lines 840 to 855 in 0986559

	# Fix static compilation with MSVC: https://bugs.exim.org/show_bug.cgi?id=1681
	# This code was taken from the CMake wiki, not from WebM.
	if(MSVC AND PCRE2_STATIC_RUNTIME)
	message(STATUS "** MSVC and PCRE2_STATIC_RUNTIME: modifying compiler flags to use static runtime library")
	foreach(
	flag_var
	CMAKE_C_FLAGS
	CMAKE_C_FLAGS_DEBUG
	CMAKE_C_FLAGS_RELEASE
	CMAKE_C_FLAGS_MINSIZEREL
	CMAKE_C_FLAGS_RELWITHDEBINFO
	)
	string(REGEX REPLACE "/MD" "/MT" ${flag_var} "${${flag_var}}")
	endforeach()
	endif()

As of #542, however, the minimum CMake version is now 3.15, which means the /MD or MT flags are now provided by CMake's CMAKE_MSVC_RUNTIME_LIBRARY variable and absent in these FLAGS variables, unless CMAKE_POLICY_DEFAULT_CMP0091 is set to OLD.

Overriding CMAKE_MSVC_RUNTIME_LIBRARY at the command line now suffices, so it is best to remove PCRE2_STATIC_RUNTIME entirely, or make it modify CMAKE_MSVC_RUNTIME_LIBRARY instead. (Setting CMAKE_POLICY_DEFAULT_CMP0091 to NEW also allows CMake 3.15 or above to apply CMAKE_MSVC_RUNTIME_LIBRARY to previous PCRE2 releases that had a lower minimum version in CMakeLists.txt.)

[NWilson]

Thank you for reporting this!

I agree with your description of the issue. Thank you for researching and linking to all the documentation so helpfully.

My preferred solution is to simply remove PCRE2_STATIC_RUNTIME, since our minimum CMake version allows us to recommend the new & better way instead.

I will make this change when I have some free time to test & document it.