pacify syntax-checks

* lib/lbitset.c, tests/c++.at: here.
* cfg.mk: Add exceptions.

cfg.mk

@@ -173,9 +173,9 @@ $(call exclude,                                                         \
   prohibit_magic_number_exit=^doc/bison.texi$$                                          \
   prohibit_magic_number_exit+=?|^tests/(conflicts|regression).at$$                      \
   prohibit_strcmp=^doc/bison\.texi|tests/local\.at$$                                    \
-  prohibit_tab_based_indentation=\.(am|mk)$$|^djgpp/|^\.git|Makefile$$  \
+  prohibit_tab_based_indentation=install-icc.sh|\.(am|mk)$$|^djgpp/|^\.git|Makefile$$   \
   require_config_h_first=^(lib/yyerror|data/(glr|yacc))\.c$$                            \
   space_before_open_paren=^(data/|djgpp/)                                               \
-  two_space_separator_in_usage=^(bootstrap)                             \
+  two_space_separator_in_usage=^(bootstrap|build-aux/install-icc.sh)                    \
   unmarked_diagnostics=^(djgpp/|doc/bison.texi$$|tests/c\+\+\.at$$)                     \
 )

tests/c++.at

@@ -453,7 +453,8 @@ AT_FULL_COMPILE([list])
 
 # Are we compiling with modern C++ enabled?
 AT_COMPILE_CXX([modern])
-AT_CHECK([./modern], [ignore], [ignore])
+here=. # Pacify cfg.mk's sc_at_parser_check.
+AT_CHECK([$here/modern], [ignore], [ignore])
 if test $at_status = 0; then
   modern=true
 else