Revert "Makefile: Add GCC config options to --enable-checking=all"

with `--enable-checking=all`, earlephilhower@ed86506 surely inhibits ICE such as:
```
/tmp/esp-quick-toolchain/repo/newlib/newlib/libc/stdlib/__exp10.c:19:20: internal compiler error: RTL check: expected code 'const_int', have 'symbol_ref' in xtensa_emit_move_sequence, at config/xtensa/xtensa.c:1079
```

by the way, however, `--enable-checking=all` reveals another issue; building stops by ICE in `.stage.LINUX.libstdcpp`:
```
In file included from /tmp/esp-quick-toolchain/arena.x86_64/gcc-gnu/xtensa-lx106-elf/libstdc++-v3/include/bits/hashtable.h:35,
                 from /tmp/esp-quick-toolchain/arena.x86_64/gcc-gnu/xtensa-lx106-elf/libstdc++-v3/include/unordered_map:46,
                 from /tmp/esp-quick-toolchain/repo/gcc-gnu/libstdc++-v3/include/precompiled/stdc++.h:117:
/tmp/esp-quick-toolchain/arena.x86_64/gcc-gnu/xtensa-lx106-elf/libstdc++-v3/include/bits/hashtable_policy.h:787:23: internal compiler error: in discriminator_for_local$
      |  __throw_out_of_range(__EXCSTR(__N("_Map_base::at")));
      |                       ^~~~~~~~
0x5fe038 discriminator_for_local_entity
        /tmp/esp-quick-toolchain/repo/gcc-gnu/gcc/cp/mangle.c:1910
(snip)
```
```
static int
discriminator_for_local_entity (tree entity)
{
  if (!DECL_LANG_SPECIFIC (entity))
    {
      /* Some decls, like __FUNCTION__, don't need a discriminator.  */
      gcc_checking_assert (DECL_ARTIFICIAL (entity));
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      return 0;
    }
  else if (tree disc = DECL_DISCRIMINATOR (entity))
    return TREE_INT_CST_LOW (disc);
  else
    /* The first entity with a particular name doesn't get
       DECL_DISCRIMINATOR set up.  */
    return 0;
}
```
(https://github.com/gcc-mirror/gcc/blob/releases/gcc-10.3.0/gcc/cp/mangle.c#L1910)

but the abovementioned issue seems not to be related to this PR and should be posted as detached issue/PR, i guess.
then, this reverts commit 0b97526.

Author: jjsuwa-sys3175

Makefile

@@ -254,7 +254,6 @@ configure += --enable-languages=c,c++
 configure += --enable-lto
 configure += --enable-static=yes
 configure += --disable-libstdcxx-verbose
-configure += --enable-checking=all
 
 # Newlib configuration common
 CONFIGURENEWLIBCOM  = --with-newlib