Fix locating of cppcheck when it is installed manually on the system.

cmake/cppcheck.cmake

@@ -21,7 +21,9 @@
 
 set(CPPCHECK_COMMAND NOTFOUND)
 find_file(CPPCHECK_COMMAND NAMES cppcheck cppcheck.exe 
-    PATHS ${CONAN_BIN_DIRS_CPPCHECK} ${CONAN_BIN_DIRS_CPPCHECK_RELEASE})
+    PATHS ${CONAN_BIN_DIRS_CPPCHECK} ${CONAN_BIN_DIRS_CPPCHECK_RELEASE} 
+    $ENV{PATH} $ENV{CPPCHECK_DIR}
+    NO_DEFAULT_PATH)
 
 if(NOT CPPCHECK_COMMAND)
   message(SEND_ERROR