Revert "[Folly] Helper method to get exception type"

Summary: This reverts commit 2c4f8da739ba0294f2c947753a0e30fee291feb5.

Test Plan: Compiles

Reviewed By: tudorb@fb.com

FB internal diff: D1108840
Detect availability of cplus_demangle_v3_callback()

Summary:
- Add autoconf check for cplus_demangle_v3_callback() in libiberty and
avoid is usage when not available. Clang/libc++ on Mac OS X doesn't
support this.

Test Plan:
- fbconfig -r folly && fbmake runtests
- ./configure && make check on Mac OS X

Reviewed By: tudorb@fb.com

FB internal diff: D1108543
folly: avoid ASAN-detected new[] vs "delete" mismatch

Summary:
* folly/test/PackedSyncPtrTest.cpp: Avoid an operator new [] vs
operator delete mismatch.

Test Plan:
fbconfig --platform-all=gcc-4.8.1-glibc-2.17 --sanitize=address \
folly/test:packed_sync_ptr_test && fbmake runtests

Reviewed By: tudorb@fb.com

FB internal diff: D1111227