Bug 944935 - Cleanup some useless AC_CHECK_FUNCS tests in configure.in. r=gps

- HAVE_RANDOM is not checked at all.
- HAVE_STRERROR is not checked in code built using the defines from the main
  configure.
- HAVE_LCHOWN is only checked in nsinstall.c, which means the test is also wrong
  since it's checking for the target instead of the host. Also, lchown is only
  used of the -o and -g options of nsinstall, which, as far as I know, we don't
  use (and if we were, that would fail with nsinstall.py, which explicitly rejects
  them).
- HAVE_FCHMOD is only checked in nsinstall.c, so same as above about the
  correctness of the check. If it's not available, nsinstall.c falls back to
  chmod, which is fine enough for our use.
- HAVE_SNPRINTF is not checked.
- HAVE_MEMMOVE is checked in parser/expat/lib/xmlparse.c, but it's also
  unconditionally defined in expat_config.h which is included from that file.
- HAVE_SETBUF is checked in a couple files, but setbuf is C89 and C99, I think
  it's safe to assume all compilers we support are C89 and C99. Interestingly,
  windows does have it, but since we skip this check on windows, we don't use it.
- HAVE_ISATTY, same as HAVE_SETBUF, except it's POSIX instead of C89/C99.
- HAVE_FLOCKFILE is not checked at all.
- HAVE_STRTOK_R is not checked.
- HAVE_FT_SELECT_SIZE is not checked.
- HAVE_DLADDR is not checked under js/src.
- HAVE_GETPAGESIZE is not checked under js/src (it is in libffi, but ffi uses
  its own configure)
- HAVE_LSTAT64, HAVE_STAT64, HAVE_STATVFS, HAVE_STATVFS64, HAVE_TRUNCATE64 are
  not checked under js/src.
- HAVE_SBRK is not checked under js/src. Moreover,
  js/src/assembler/wtf/Platform.h defines it depending on the platform.
- HAVE_SNPRINTF is not checked under js/src.
- HAVE_HYPOT is not checked under js/src.
- HAVE__UNWIND_BACKTRACE is not checked under js/src.

ipc/testshell/XPCShellEnvironment.cpp

@@ -309,10 +309,7 @@ XPCShellEnvironment::ProcessFile(JSContext *cx,
     if (forceTTY) {
         file = stdin;
     }
-    else
-#ifdef HAVE_ISATTY
-    if (!isatty(fileno(file)))
-#endif
+    else if (!isatty(fileno(file)))
     {
         /*
          * It's not interactive - just execute it.
@@ -475,11 +472,9 @@ XPCShellEnvironment::Init()
 {
     nsresult rv;
 
-#ifdef HAVE_SETBUF
     // unbuffer stdout so that output is in the correct order; note that stderr
     // is unbuffered by default
     setbuf(stdout, 0);
-#endif
 
     nsCOMPtr<nsIJSRuntimeService> rtsvc =
         do_GetService("@mozilla.org/js/xpc/RuntimeService;1");