Fixed some warnings reported by clang.
-Wnewline-eof
no newline at end of file
-Wc++98-compat-extra-semi
extra ';' outside of a function is incompatible with C++98
-Winconsistent-missing-destructor-override
'~XXX' overrides a destructor but is not marked 'override'
-Wheader-hygiene
using namespace directive in global context in header
-Wunused-parameter
unused parameter
Fixed some warnings reported by gcc.
-Werror=missing-field-initializers
missing initializer for member ‘opentelemetry::v1::sdk::trace::SamplingResult::trace_state’
-Werror=unused-variable
unused variable
-Werror=unused-parameter
unused parameter