Fix correct name for Standard/reference architecture

These functions (enabled when -ffast-math is used) were only added
in glibc 2.15. However, SLC 6 still uses glibc 2.12 and clang does
not check before emitting the symbols, so linkage with clang is
broken when fast math is enabled.

Add possibilities to pass options in TH1::Merge
Print a warning in case of duplicate labels.
Add an option to force merge numeric (bin centre by bin center values)  and an option to skip duplicate labels check, which can be quite expensive in term of CPU time

This works around an ABI compatibility issue between cling and gcc
on 32bit machines in which they disagree in the way arguments should
be passed to such a function.

(cherry picked from commit ba4a8f21)

This check does more harm than good.

this allows to avoid missing symbols when running macros.

Fixes coverity 98288.

Fixes coverity 98293, 98292, 98290, 98287, 98279.

and update the documentation to the new behaviours, e.g. lazyness of cache, possible lazyness of Snapshot, Report is now an action.

The double-decrement was causing *some* operations to not be interruptible,
specifically those that had recursive ProcessLine() invocations, e.g. from PluginManager.

now Snapshot accepts to identify columns:
- A regex as a string_view
- A vector<string>
- A initializer_list<string>

This allows users to invoke it as follows:
1. tdf.Snapshot("t", filename, "an*");
2. tdf.Snapshot("t", filename, {"ans"});
3. tdf.Snapshot("t", filename, {{"ans"}});