[CMake] autoconf AC_REPLACE_FUNCS replacement for CMake

[Thomas Klausner]

Hi!

In autoconf there's a useful macro: AC_REPLACE_FUNCS.
It's called like:
	AC_REPLACE_FUNCS([fct1 fct2...])
It tests for the existence of the arguments, and if they
are missing, adds fct1.c (etc.) to the sources used for
building.

I wrote a replacement macro for CMake:
MACRO(REPLACE_FUNCTIONS sources)
  FOREACH(name ${ARGN})
    STRING(TOUPPER have_${name} SYMBOL_NAME)
    CHECK_FUNCTION_EXISTS(${name} ${SYMBOL_NAME})
    IF(NOT ${SYMBOL_NAME})
      SET(${sources} ${${sources}} ${name}.c)
    ENDIF(NOT ${SYMBOL_NAME})
  ENDFOREACH(name)
ENDMACRO(REPLACE_FUNCTIONS)

It's called like this:
REPLACE_FUNCTIONS(LIB_SOURCES err errx poll strlcpy warn warnx)
If the system doesn't provide err(), "err.c" is added to
LIB_SOURCES (and similarly for the other functions).

Feel free to use it for whatever you want.

Improvements are of course welcome too!

Cheers,
 Thomas