[BUILD] Fix compiling problems for gcc 4.8

[owent]

Fixes #3099

Changes

Fix remaining issues preventing a C++11 build with gcc 4.8.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[netlify]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.81%. Comparing base (497eaf4) to head (d4531be).
Report is 142 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3100      +/-   ##
==========================================
+ Coverage   87.12%   87.81%   +0.69%     
==========================================
  Files         200      195       -5     
  Lines        6109     5969     -140     
==========================================
- Hits         5322     5241      -81     
+ Misses        787      728      -59     

Files with missing lines	Coverage Δ
exporters/memory/src/in_memory_metric_data.cc	85.00% <100.00%> (ø)
...rs/memory/src/in_memory_metric_exporter_factory.cc	100.00% <100.00%> (ø)

... and 125 files with indirect coverage changes

[marcalff]

LGTM.