FindOpenSSL: Add support for static MSVC runtime

Add an OPENSSL_MSVC_STATIC_RT option to switch from the default search
for `/MD` libraries to look for `/MT` libraries instead.

Help/release/dev/FindOpenSSL-msvc-static-rt.rst

@@ -0,0 +1,6 @@
+FindOpenSSL-msvc-static-rt
+--------------------------
+
+* The :module:`FindOpenSSL` module gained a new
+  ``OPENSSL_MSVC_STATIC_RT`` option to search for libraries using
+  the MSVC static runtime.

Modules/FindOpenSSL.cmake

@@ -37,6 +37,7 @@
 #
 # Set ``OPENSSL_ROOT_DIR`` to the root directory of an OpenSSL installation.
 # Set ``OPENSSL_USE_STATIC_LIBS`` to ``TRUE`` to look for static libraries.
+# Set ``OPENSSL_MSVC_STATIC_RT`` set ``TRUE`` to choose the MT version of the lib.
 
 #=============================================================================
 # Copyright 2006-2009 Kitware, Inc.
@@ -113,7 +114,7 @@ if(WIN32 AND NOT CYGWIN)
     # /MD and /MDd are the standard values - if someone wants to use
     # others, the libnames have to change here too
     # use also ssl and ssleay32 in debug as fallback for openssl < 0.9.8b
-    # TODO: handle /MT and static lib
+    # enable OPENSSL_MSVC_STATIC_RT to get the libs build /MT (Multithreaded no-DLL)
     # In Visual C++ naming convention each of these four kinds of Windows libraries has it's standard suffix:
     #   * MD for dynamic-release
     #   * MDd for dynamic-debug
@@ -126,6 +127,12 @@ if(WIN32 AND NOT CYGWIN)
     # ssleay32MD.lib is identical to ../ssleay32.lib
     # enable OPENSSL_USE_STATIC_LIBS to use the static libs located in lib/VC/static
 
+    if (OPENSSL_MSVC_STATIC_RT)
+      set(_OPENSSL_MSVC_RT_MODE "MT")
+    else ()
+      set(_OPENSSL_MSVC_RT_MODE "MD")
+    endif ()
+
     if(OPENSSL_USE_STATIC_LIBS)
       set(_OPENSSL_PATH_SUFFIXES
         "lib"
@@ -142,7 +149,7 @@ if(WIN32 AND NOT CYGWIN)
 
     find_library(LIB_EAY_DEBUG
       NAMES
-        libeay32MDd
+        libeay32${_OPENSSL_MSVC_RT_MODE}d
         libeay32d
       ${_OPENSSL_ROOT_HINTS_AND_PATHS}
       PATH_SUFFIXES
@@ -151,7 +158,7 @@ if(WIN32 AND NOT CYGWIN)
 
     find_library(LIB_EAY_RELEASE
       NAMES
-        libeay32MD
+        libeay32${_OPENSSL_MSVC_RT_MODE}
         libeay32
       ${_OPENSSL_ROOT_HINTS_AND_PATHS}
       PATH_SUFFIXES
@@ -160,7 +167,7 @@ if(WIN32 AND NOT CYGWIN)
 
     find_library(SSL_EAY_DEBUG
       NAMES
-        ssleay32MDd
+        ssleay32${_OPENSSL_MSVC_RT_MODE}d
         ssleay32d
       ${_OPENSSL_ROOT_HINTS_AND_PATHS}
       PATH_SUFFIXES
@@ -169,7 +176,7 @@ if(WIN32 AND NOT CYGWIN)
 
     find_library(SSL_EAY_RELEASE
       NAMES
-        ssleay32MD
+        ssleay32${_OPENSSL_MSVC_RT_MODE}
         ssleay32
         ssl
       ${_OPENSSL_ROOT_HINTS_AND_PATHS}