Clang has a nice page describing the project status w.r.t. C++1z/C++17 feature support (and C++11 and C++14, it\'s the same page).
g++ has a page regarding C++14 feature
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".typename
for template template parameters since 5.1.0static_assert
without a message in HEADu8
character literals in HEADUnsupported (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.