* m4/logf-ieee.m4: New file.
* m4/logf.m4 (gl_FUNC_LOGF): If gl_FUNC_LOGF_IEEE is present, test
whether logf works with a negative argument. Replace it if not.
* lib/logf.c (logf): For negative arguments, return NaN.
* modules/logf-ieee (Files): Add m4/logf-ieee.m4.
(configure.ac): Invoke gl_FUNC_LOGF_IEEE.
* doc/posix-functions/logf.texi: Mention the logf-ieee module.
* lib/math.in.h (logf): Override if REPLACE_LOGF is 1.
* lib/logf.c (logf): If logf exists, use it and provide just the
workaround.
* m4/logf.m4 (gl_FUNC_LOGF_WORKS): New macro.
(gl_FUNC_LOGF): Invoke it. Set REPLACE_LOGF.
* m4/math_h.m4 (gl_MATH_H_DEFAULTS): Initialize REPLACE_LOGF.
* modules/math (Makefile.am): Substitute REPLACE_LOGF.
* modules/logf (configure.ac): Consider REPLACE_LOGF.
(Depends-on): Update conditions.
* doc/posix-functions/logf.texi: Mention the OSF/1 5.1 problem.
* lib/math.in.h (logf): New declaration.
* lib/logf.c: New file.
* m4/logf.m4: New file.
* m4/math_h.m4 (gl_MATH_H): Test whether logf is declared.
(gl_MATH_H_DEFAULTS): Initialize GNULIB_LOGF, HAVE_LOGF.
* modules/math (Makefile.am): Substitute GNULIB_LOGF, HAVE_LOGF.
* modules/logf: New file.
* tests/test-math-c++.cc: Check the declaration of logf.
* doc/posix-functions/logf.texi: Mention the new module.
