allow linking against the static msvc runtime library (#133)

allow linking against the static msvc runtime library

CMakeLists.txt

@@ -36,6 +36,27 @@ OPTION (CARES_SHARED     "Build as a shared library"
 OPTION (CARES_INSTALL    "Create installation targets (chain builders may want to disable this)" ON)
 OPTION (CARES_STATIC_PIC "Build the static library as PIC (position independent)"                OFF)
 
+# allow linking against the static runtime library in msvc
+IF (MSVC)
+	OPTION (CARES_MSVC_STATIC_RUNTIME "Link against the static runtime library" OFF)
+	IF (CARES_MSVC_STATIC_RUNTIME)
+		# CMAKE_CONFIGURATION_TYPES is empty on non-IDE generators (Ninja, NMake)
+		# and that's why we also use CMAKE_BUILD_TYPE to cover for those generators.
+		# For IDE generators, CMAKE_BUILD_TYPE is usually empty
+		FOREACH (config_type ${CMAKE_CONFIGURATION_TYPES} ${CMAKE_BUILD_TYPE})
+			STRING (TOUPPER ${config_type} upper_config_type)
+			SET (flag_var "CMAKE_C_FLAGS_${upper_config_type}")
+			IF (${flag_var} MATCHES "/MD")
+				STRING (REGEX REPLACE "/MD" "/MT" ${flag_var} "${${flag_var}}")
+			ENDIF ()
+		ENDFOREACH ()
+
+		# clean up
+		SET (upper_config_type)
+		SET (config_type)
+		SET (flag_var)
+	ENDIF ()
+ENDIF ()
 
 # Keep build organized.
 SET (CMAKE_RUNTIME_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR}/bin)