Add support for use of static MSVC runtimes

In certain contexts LibreSSL needs to be built with `/MT` instead of `/MD` for inclusion in other projects. These changes allow for the command-line option `USE_STATIC_MSVC_RUNTIMES` to be set to `ON` if the use wishes to generate projects that will build with static runtimes.

This feature requires CMAKE version 3.15+, hence the minimum required version has changed as well.

1 files changed, 7 insertions, 1 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index e198f7c..a577d29 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required (VERSION 3.0)
+cmake_minimum_required (VERSION 3.15)
 include(CheckFunctionExists)
 include(CheckSymbolExists)
 include(CheckLibraryExists)
@@ -9,6 +9,7 @@ set(CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}" ${CMAKE_MODULE_PATH})
 include(cmake_export_symbol)
 include(GNUInstallDirs)
 
+cmake_policy(SET CMP0091 NEW)
 project (LibreSSL C ASM)
 
 enable_testing()
@@ -36,6 +37,11 @@ option(ENABLE_EXTRATESTS "Enable extra tests that may be unreliable on some plat
 option(ENABLE_NC "Enable installing TLS-enabled nc(1)" OFF)
 set(OPENSSLDIR ${OPENSSLDIR} CACHE PATH "Set the default openssl directory" FORCE)
 
+option(USE_STATIC_MSVC_RUNTIMES "Use /MT instead of /MD in MSVC" OFF)
+if( USE_STATIC_MSVC_RUNTIMES )
+    set(CMAKE_MSVC_RUNTIME_LIBRARY "MultiThreaded$<$<CONFIG:Debug>:Debug>")
+endif()
+
 if(NOT LIBRESSL_SKIP_INSTALL)
         set( ENABLE_LIBRESSL_INSTALL ON )
 endif(NOT LIBRESSL_SKIP_INSTALL)