Automatically detected using clang-tidy with bugprone-reserved-identifier
check.

By the way, homogeneize the define identifiers in relation to camel case
convention.

Automatically detected using clang-tidy with modernize-use-nodiscard check.

Initialization with initalizer list is nicer. And, more importantly,
initialization with parentheses is not supported by Clang < 16.

This is unsafe since the find() method can return a past-the-end iterator,
which should be tested for.

Replace most instances by calls to the std::map::at() method (which throws if
the key is unknown), and which is incidentally more readable.

By the way, turn those classes into structs since all their members are public.

Otherwise clang emits this warning:
 using directive refers to implicitly-defined namespace 'std'

The syntax makes clearer the distinction between a function call and an
initialization. Also, it prevents bugs due to implicit type conversions.

For a rationale, see http://www.sjbrown.co.uk/2004/05/01/always-use-explicit/

This was not conceptually an enum, but rather a collection of unrelated
constants:
- two constants for use as placeholder for symbol IDs at different places
- one constant for the default number of arguments

Those were not automatically replaced by clang-tidy, I don’t know why…

Performed using modernize-use-noexcept from clang-tidy.

https://clang.llvm.org/extra/clang-tidy/checks/modernize-use-noexcept.html

Performed using modernize-use-auto from clang-tidy.

https://clang.llvm.org/extra/clang-tidy/checks/modernize-use-auto.html

Performed using modernize-loop-convert from clang-tidy.

Manual intervention was needed in MacroValue.cc because of a variable name
capture issue.

https://clang.llvm.org/extra/clang-tidy/checks/modernize-loop-convert.html

This reverts commit 28ffa9c56fd021cc75415aeafc13d3810d1b3132, reversing
changes made to 60b3577a09f3eb9cf3cc590241343b1f0fee8706.

Conflicts:
	preprocessor/Shocks.cc
	preprocessor/SymbolTable.cc

This reverts commit def2bf81d2b8dacda4b72d4250020eb793f28b20.