Fix clang compilation for tests dep 'cppdotenv'

[JavierJF]

Minimal changes for fixing the cppdotenv compilation under clang. Removes an unnecessary using directive since fully qualified names are used within the file anyway.

Extra details

There is another potential solution, that involves fixing all the ambiguities that arise when the namespace is included in the global one by the using directive. Several changes are required within the same file, for fixing these ambiguities, clang appears more sensitive that gcc and requires a full path from global namespace :: for being able to do proper name resolution. It's left here as no more than an interesting read:

nm_clang_fix_fqualified.txt

[mirostauder]

added fixes based on CLang warnings:

• wrong comparisons
• wrong bracketing
• wrong types
• wrong format strings
• missing c_str() conversion
• missing type casts
• pointer arithmetic
• bad function call

other:

• compiler calls via $(CXX)
• privileged containers
• ASAN/ASLR limitation workaround

ASAN breaks with ASLR > 28bits used by recent kernels https://github.com/google/sanitizers/issues/1716

[mirostauder]

retest this please