Fix cross-compilation and MSVC build with OpenSSL

When building for multiple platforms I encountered several issues.
Fist of all MSVC (Windows) build with TLS support through OpenSSL
requires additional library "crypt32".
Secondly, detection of pthread library failed when a cross-compiler
was used (target platform is not identical to source/build platform).
The "FIND_PACKAGE(Threads)" works fine but "FIND_LIBRARY(...)"
either fails or finds pthread library for the wrong platform.
It seems to methat presence of "CMAKE_THREAD_LIBS_INIT" which
is set by the "FIND_PACKAGE(Threads)" test is a sufficiently
reliable to use it to set "VMIME_HAVE_PTHREAD" but I must admit
that this is not really my cup of coffee :-)

CMakeLists.txt

@@ -678,6 +678,10 @@ IF(VMIME_HAVE_TLS_SUPPORT)
 			)
 		ENDIF()
 
+		IF(WIN32)
+			SET(CMAKE_CXX_STANDARD_LIBRARIES "${CMAKE_CXX_STANDARD_LIBRARIES} crypt32.lib")
+		ENDIF()
+
 		SET(VMIME_PKGCONFIG_REQUIRES "${VMIME_PKGCONFIG_REQUIRES} openssl")
 
 		SET(VMIME_TLS_SUPPORT_LIB_IS_GNUTLS "OFF")
@@ -958,9 +962,9 @@ IF(VMIME_BUILD_SHARED_LIBRARY)
 	)
 ENDIF()
 
-FIND_LIBRARY(PTHREAD_LIB pthread)
+#FIND_LIBRARY(PTHREAD_LIB pthread)
 
-IF(PTHREAD_LIB)
+IF(CMAKE_THREAD_LIBS_INIT)
 	SET(VMIME_HAVE_PTHREAD 1)
 
 	IF(VMIME_BUILD_SHARED_LIBRARY)
@@ -1007,6 +1011,9 @@ IF("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
 	#SET(CMAKE_EXE_LINKER_FLAGS "-s")
 
 ELSE()
+	IF("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC")
+		SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /MP /EHsc")
+	ENDIF()
 
 	IF(CMAKE_COMPILER_IS_GNUCC OR CMAKE_COMPILER_IS_GNUCXX)