Merge pull request #155 from cmourglia/develop

Pure C projects had errors in detect_vs_runtime()

conan.cmake

@@ -298,14 +298,16 @@ function(conan_cmake_detect_vs_runtime result)
     string(TOUPPER ${CMAKE_BUILD_TYPE} build_type)
     set(variables CMAKE_CXX_FLAGS_${build_type} CMAKE_C_FLAGS_${build_type} CMAKE_CXX_FLAGS CMAKE_C_FLAGS)
     foreach(variable ${variables})
-        string(REPLACE " " ";" flags ${${variable}})
-        foreach (flag ${flags})
-            if(${flag} STREQUAL "/MD" OR ${flag} STREQUAL "/MDd" OR ${flag} STREQUAL "/MT" OR ${flag} STREQUAL "/MTd")
-                string(SUBSTRING ${flag} 1 -1 runtime)
-                set(${result} ${runtime} PARENT_SCOPE)
-                return()
-            endif()
-        endforeach()
+        if(NOT "${${variable}}" STREQUAL "")
+            string(REPLACE " " ";" flags ${${variable}})
+            foreach (flag ${flags})
+                if(${flag} STREQUAL "/MD" OR ${flag} STREQUAL "/MDd" OR ${flag} STREQUAL "/MT" OR ${flag} STREQUAL "/MTd")
+                    string(SUBSTRING ${flag} 1 -1 runtime)
+                    set(${result} ${runtime} PARENT_SCOPE)
+                    return()
+                endif()
+            endforeach()
+        endif()
     endforeach()
     if(${build_type} STREQUAL "DEBUG")
         set(${result} "MDd" PARENT_SCOPE)