Remove --enable-tunables configure option

And make always supported.  The configure option was added on glibc 2.25
and some features require it (such as hwcap mask, huge pages support, and
lock elisition tuning).  It also simplifies the build permutations.

Changes from v1:
 * Remove glibc.rtld.dynamic_sort changes, it is orthogonal and needs
   more discussion.
 * Cleanup more code.
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

elf/dl-support.c

@@ -168,16 +168,6 @@ enum dso_sort_algorithm _dl_dso_sort_algo;
 /* The value of the FPU control word the kernel will preset in hardware.  */
 fpu_control_t _dl_fpu_control = _FPU_DEFAULT;
 
-#if !HAVE_TUNABLES
-/* This is not initialized to HWCAP_IMPORTANT, matching the definition
-   of _dl_important_hwcaps, below, where no hwcap strings are ever
-   used.  This mask is still used to mediate the lookups in the cache
-   file.  Since there is no way to set this nonzero (we don't grok the
-   LD_HWCAP_MASK environment variable here), there is no real point in
-   setting _dl_hwcap nonzero below, but we do anyway.  */
-uint64_t _dl_hwcap_mask;
-#endif
-
 /* Prevailing state of the stack.  Generally this includes PF_X, indicating it's
  * executable but this isn't true for all platforms.  */
 ElfW(Word) _dl_stack_flags = DEFAULT_STACK_PERMS;
@@ -328,11 +318,6 @@ _dl_non_dynamic_init (void)
 	  __unsetenv (cp);
 	  cp = strchr (cp, '\0') + 1;
 	}
-
-#if !HAVE_TUNABLES
-      if (__access ("/etc/suid-debug", F_OK) != 0)
-	__unsetenv ("MALLOC_CHECK_");
-#endif
     }
 
 #ifdef DL_PLATFORM_INIT