[toplevel] remove tentative_cc

[Joseph S. Myers]

I see there's more than just tentative_cc that tries to deal with compiler 
settings in ways that should be the responsibility of autoconf.  There's 
the

# Make sure that the compiler is able to generate an executable.  If it
# can't, we are probably in trouble.  We don't care whether we can run the
# executable--we might be using a cross compiler--we only care whether it
# can be created.  At this point the main configure script has set CC.

code - and there's probably a better autoconf-native way of testing that 
the compiler can link an executable than the shell code here.  And that's 
immediately followed by

# The Solaris /usr/ucb/cc compiler does not appear to work.

which is surely outside what the script ought to be doing.  I don't think 
the

# hpux11 in 64bit mode has libraries in a weird place.  Arrange to find
# them automatically.

code makes any sense now either; autoconf knows about /usr/X11R6/include 
if you use the right macros, while GCC appears to have known to search in 
/usr/lib/pa20_64 for this target since at least 2004.

-- 
Joseph S. Myers
joseph@codesourcery.com