When it compiles Fortran source and emits object code, LF95 converts the names of all entry points and external references into all lower case letters, and attaches an underscore (_) symbol to both the front and back of each such name. FCC does not change the case of names, but it does add a leading underscore to each one.
Therefore, if a Fortran program calls a subroutine named "CLOUD", LF95 will generate a requirement for an external symbol called "_cloud_". If the subroutine is written in C, and compiled by FCC, then the entry point name must be "cloud_". (Note the absence of a leading underscore, which will be added by FCC.)