folly: accommodate use of -Wshadow in other projects

folly: accommodate use of -Wshadow in other projects

Summary:
Without this change, any folly-using project that attempts to enable
gcc's -Wshadow option will be overwhelmed by warnings about violations
in folly's class definitions.  Violations are often due to local
variable or parameter names shadowed by a member function.

Bracket offending content with directives like this:

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wshadow"
...
#pragma GCC diagnostic pop

This set of modified files is the minimal set to allow tao
to use -Wshadow with no folly-related warning.

Test Plan:
fbmake folly/test && fbmake opt

Reviewed By: simpkins@fb.com

FB internal diff: D848455