ditch an ugly workaround for rhel5

test "x$ac_cv_prog_cc_c99" = "x" breaks autoconf for compilers which do not need
any extra arguments to support c99.

Partly addresses #2047

configure.ac

@@ -25,22 +25,6 @@ AC_PROG_LIBTOOL
 AC_GNU_SOURCE
 AC_PROG_CC
 AC_PROG_CC_STDC
-if test "x$ac_cv_prog_cc_c99" = "xno" || test "x$ac_cv_prog_cc_c99" = "x"; then
-# We might be on RHEL5 with a git checkout and so broken
-# autoconf. Check if CC is gcc and if it bails when given -std=gnu99.
-# If not, use that.  Yuck.
-  if test "x$ac_cv_c_compiler_gnu" = "xyes"; then
-     CC="$CC -std=gnu99"
-     AC_RUN_IFELSE(
-	[AC_LANG_PROGRAM([],[[
-return 0;
-    ]])],
-    [],
-    [AC_MSG_ERROR([Could not find a C99 compatible compiler])])
-  else
-    AC_MSG_ERROR([Could not find a C99 compatible compiler])
-  fi
-fi
 AC_PROG_CPP
 
 AX_PTHREAD(,[AC_MSG_ERROR([Could not configure pthreads support])])