Try to use a more modern g++.

.travis.yml

@@ -9,11 +9,11 @@ addons:
       sources:
         - ubuntu-toolchain-r-test
       packages:
-        - gcc-4.9
-        - g++-4.9
-env:
-  - MATRIX_EVAL="CC=gcc-4.9 && CXX=g++-4.9"
+        - gcc-7
+        - g++-7
 script:
+  - export CC=gcc-7
+  - export CXX=g++-7
   - cargo fmt --all -- --check
   - cargo build --verbose
   - cargo test --verbose

test.py

@@ -48,7 +48,7 @@ def gxx(src):
     if gxx_bin == None:
         gxx_bin = 'g++'
 
-    subprocess.check_output([gxx_bin, "-D", "DEFINED", "-std=c++11", "-c", src, "-o", "tests/expectations/tmp.o"])
+    subprocess.check_output([gxx_bin, "-D", "DEFINED", "-std=c++17", "-c", src, "-o", "tests/expectations/tmp.o"])
     os.remove("tests/expectations/tmp.o")
 
 def run_compile_test(rust_src, verify, c, style=""):