Add a check of MSVC variable before setting flags that link the libra… (#814)

* Add a check of MSVC variable before setting flags that link the library with the MSVC static runtime

* Move MSVC guard inside the 'foreach' loop used to force static runtime link
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5d8885d..12a7938 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -317,8 +317,10 @@
         CMAKE_C_FLAGS_DEBUG CMAKE_C_FLAGS_DEBUG_INIT
         CMAKE_CXX_FLAGS_RELEASE  CMAKE_CXX_FLAGS_RELWITHDEBINFO
         CMAKE_CXX_FLAGS_DEBUG  CMAKE_CXX_FLAGS_DEBUG_INIT)
-        STRING(REPLACE "/MD"  "/MT" "${flag}" "${${flag}}")
-        SET("${flag}" "${${flag}} /EHsc")
+        if (MSVC)
+            STRING(REPLACE "/MD"  "/MT" "${flag}" "${${flag}}")
+            SET("${flag}" "${${flag}} /EHsc")
+        endif (MSVC)
     ENDFOREACH()
 endif ()