Remove PCRE2_STATIC_RUNTIME (#753)

Since we have raised our minimum CMake version to 3.15, this updates the
default value of the "CMP0091" backwards-compatibility policy, such that
PCRE2_STATIC_RUNTIME is now broken (since 10.45	when
cmake_minimum_required was increased).

We can remove this flag, since the new built-in
CMAKE_MSVC_RUNTIME_LIBRARY provides the same behaviour.

Author: NWilson

.github/workflows/dev.yml

@@ -260,7 +260,7 @@ jobs:
           submodules: true
 
       - name: Configure
-        run: cmake $CMAKE_FLAGS -DPCRE2_SUPPORT_JIT=ON -DPCRE2_BUILD_PCRE2_16=ON -DPCRE2_BUILD_PCRE2_32=ON -DPCRE2GREP_SUPPORT_CALLOUT_FORK=OFF -DPCRE2_DEBUG=ON -DPCRE2_NEWLINE=ANYCRLF -DPCRE2_STATIC_PIC=ON -DPCRE2_STATIC_RUNTIME=ON -DPCRE2_SUPPORT_BSR_ANYCRLF=ON -DBUILD_SHARED_LIBS=OFF -DBUILD_STATIC_LIBS=ON -DCMAKE_C_FLAGS="$CFLAGS_MSVC" -DCMAKE_COMPILE_WARNING_AS_ERROR=ON -B build -A Win32
+        run: cmake $CMAKE_FLAGS -DPCRE2_SUPPORT_JIT=ON -DPCRE2_BUILD_PCRE2_16=ON -DPCRE2_BUILD_PCRE2_32=ON -DPCRE2GREP_SUPPORT_CALLOUT_FORK=OFF -DPCRE2_DEBUG=ON -DPCRE2_NEWLINE=ANYCRLF -DPCRE2_STATIC_PIC=ON -DPCRE2_SUPPORT_BSR_ANYCRLF=ON -DBUILD_SHARED_LIBS=OFF -DBUILD_STATIC_LIBS=ON -DCMAKE_C_FLAGS="$CFLAGS_MSVC" -DCMAKE_COMPILE_WARNING_AS_ERROR=ON -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded -B build -A Win32
 
       - name: Build
         run: cmake --build build --config RelWithDebInfo

CMakeLists.txt

@@ -421,7 +421,6 @@ if(MINGW)
 endif()
 
 if(MSVC)
-  option(PCRE2_STATIC_RUNTIME "ON=Compile against the static runtime (/MT)." OFF)
   option(INSTALL_MSVC_PDB "ON=Install .pdb files built by MSVC, if generated" OFF)
 endif()
 
@@ -846,23 +845,6 @@ if(MSVC AND BUILD_SHARED_LIBS)
   endif()
 endif()
 
-# 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()
-
 # Build setup
 
 add_compile_definitions(HAVE_CONFIG_H)