There is some support already; The following two summaries are oriented on Clang's list:
Supported (as of July 5th, 2015):
auto
for function parameters is supported since 4.9. This feature is currently considered an extension but is included in the concepts proposal and called "generic functions".
- trigraphs are being ignored by default since 5.1.0
typename
for template template parameters since 5.1.0
- new deduction rules for direct-list-initialization since 5.1.0
static_assert
without a message in HEAD
u8
character literals in HEAD
- Attributes for namespaces or enumerators in HEAD
Unsupported (as of July 5th, 2015; with links to a valid example usage):
For the status of implementation of library proposals in libstdc++, the corresponding manual has a list.