PR28901 Add two levels for -Wunused-const-variable.
There is some controversy about enabling -Wunused-const-variable for all
unused static const variables because some feel there are too many errors
exposed in header files. Create two levels for -Wunused-const-variable.
One level to only check for unused static const variables in the main
compilation file. Which is enabled by -Wunused-variable. And a second
level that also checks for unused static const variables in included
files. Which must be explicitly enabled.
gcc/ChangeLog
PR c/28901
* cgraphunit.c (check_global_declaration): Check level of
warn_unused_const_variable and main_input_filename.
* doc/invoke.texi (Warning Options): Add -Wunused-const-variable=.
(-Wunused-variable): For C implies -Wunused-const-variable=1.
(-Wunused-const-variable): Explain levels 1 and 2.
gcc/c-family/ChangeLog
PR c/28901
* c.opt (Wunused-const-variable): Turn into Alias for...
(Wunused-const-variable=): New option.
gcc/testsuite/ChangeLog
PR c/28901
* gcc.dg/unused-variable-3.c: New test.