make: unit-tests use .OBJDIR when appropriate

Always use .OBJDIR to refer to the directory make is running in.
Also, add some final filtering to cleanup references to /usr/obj

Reviewed by: rillig

make: consistently use double quotes in error messages

Previously, some error messages used single quotes, very few used
backticks or parentheses, most already used double quotes.

While here, reword a few error messages to be clearer or more consistent
with related error messages.

make: use '"filename" line 123' for locations instead of 'filename:123'

The format 'filename:123' is commonly used for identifying a location in
a file. Text editors recognize it and allow quick navigation through it.
The previous format was specific to make and would have required custom
support in editors.

The new format was already used in stack traces, except for the first
line. Now all lines use the same format.

branches: 1.3.2;
make: add more details to error message about invalid lines

tests/make: add a few more tests

make(1): add tests for the various .include directives