[Bug bootstrap/54419] [4.8 Regression] Compiling libstdc++-v3/src/c++11/random.cc fails on platforms not knowing rdrand

["howarth at nitro dot med.uc.edu" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54419

--- Comment #43 from Jack Howarth <howarth at nitro dot med.uc.edu> 2012-09-06 14:31:53 UTC ---
(In reply to comment #42)
> Sorry if I'm saying something naive - I didn't follow the whole discussion -
> but I don't understand why - assuming indeed we want to do something at
> configure time - are being attached patches directly touching
> libstdc++-v3/configure* files, instead of acinclude.m4 (to be processed by
> autoreconf), which is the normal way we write this kind of code in the
> libraries.

Probably because...

  AC_TRY_COMPILE(, [
#if !defined __LONG_DOUBLE_128__ || (defined(__sparc__) && defined(__arch64__))
#error no need for long double compatibility
#endif
  ], [ac_ldbl_compat=yes], [ac_ldbl_compat=no])
  if test "$ac_ldbl_compat" = yes; then
    AC_DEFINE([_GLIBCXX_LONG_DOUBLE_COMPAT],1,
              [Define if compatibility should be provided for
-mlong-double-64.])
   
port_specific_symbol_files="\$(top_srcdir)/config/os/gnu-linux/ldbl-extra.ver"
  fi

already existed immediately above the new test in configure.ac.