package: various fixes for syntax-check

* cfg.mk: Disable checks where needed (e.g., we do want to check the
behavior with tabs).
(sc_at_parser_check): Remove.  Unfortunately since
a11c144609 we no longer use the './'
prefix to run programs in the current directory.  That was so that we
could run Java programs like the other, although they are no run with
the `./` prefix (see 967a59d2c0).
As a consequence this sc check no longer makes sense.
However, since now AT_PARSER_CHECK passes the `./` prefix itself, this
sc-check was superfluous.
* examples/c/reccalc/scan.l: Use memcpy, not strncpy.
* src/ielr.c, src/reader.c: Obfuscate "lr(0)" so that the sc-check for
"space before paren" does not fire.
* tests/diagnostics.at: Avoid space-tab, use tab-tab.

tests/diagnostics.at

@@ -223,13 +223,13 @@ input.y: <warning>warning:</warning> fix-its can be applied.  Rerun with option
 
 AT_TEST([[Locations from M4]],
 [[%define api.prefix		{sun}
-%define api.prefix      	{🌞}
+%define api.prefix		{🌞}
 %%
 exp:;
 ]],
 [1],
 [[input.y:10.1-35: <error>error:</error> %define variable 'api.prefix' redefined
-   10 | <error>%define api.prefix      	{🌞}</error>
+   10 | <error>%define api.prefix		{🌞}</error>
       | <error>^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~</error>
 input.y:9.1-37:      previous definition
     9 | <note>%define api.prefix		{sun}</note>