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.

make: on error, print the targets to be made

This helps to understand situations with several nested sub-makes in
varying directories.

branches: 1.13.2;
tests/make: clean up, explain and reorganize several tests

tests/make: use proper variable names in short-circuit test

The previous variable names V42, V66, iV1 and iV2 didn't carry enough
information to be readily readable, making the test hard to understand.

Rename the variables to be more expressive. While here, properly
explain what happened behind the scenes in 2020 and how the evaluation
of conditions was fixed after discovering the actual cause of the
unexpected error messages.

make(1): adjust condition descriptions in test cond-short

Before, the conditions in the output had been expanded, which made them
illegible. The expanded conditions were unrealistic as well since the
evaluation flags differ between a condition and normal evaluation
(VARE_WANTRES, VARE_UNDEFERR).

compare_expression: return after fetch lhs and rhs if !doEval

Otherwise we end up throwing warings/errors for valid
conditionals due to not expanding variables fully.

Add tests to catch this.

Reviewed by: rillig

make(1): fix unnecessary evaluation of variables in :@var@ modifier

make(1): fix unnecessary evaluation for :S :C := modifiers

make(1): demonstrate some more cases for unintended evaluation

make(1): fix unnecessary evaluation of :M and :N modifiers

make(1): demonstrate another unintended variable evaluation

make(1): fix edge case for evaluating unnecessary conditions

make(1): demonstrate another unnecessary condition evaluation

make(1): fix evaluation of unreachable conditions

Since 2015-10-11, make had evaluated unreachable conditions even though
the manual page said it didn't.

make(1): demonstrate bug when evaluating conditions