gnu: vte-ng: Update to 0.56.2.a.

* gnu/packages/gnome.scm (vte-ng): Update to 0.56.2.a.
[native-inputs]: Add GCC-7.
[arguments]: Add GCC7 workaround.

gnu/packages/gnome.scm

@@ -2324,7 +2324,7 @@ editors, IDEs, etc.")
   (package
     (inherit vte)
     (name "vte-ng")
-    (version "0.54.2.a")
+    (version "0.56.2.a")
     (home-page "https://github.com/thestinger/vte-ng")
     (source (origin
               (method git-fetch)
@@ -2332,10 +2332,11 @@ editors, IDEs, etc.")
               (file-name (git-file-name name version))
               (sha256
                (base32
-                "1r7d9m07cpdr4f7rw3yx33hmp4jmsk0dn5byq5wgksb2qjbc4ags"))))
+                "1lmba6i0abifmvvfb1q63ql6zh6d38148kp6skmkggiib2hi5dki"))))
     (native-inputs
      `(("gtk-doc" ,gtk-doc)
        ("gperf" ,gperf)
+       ("gcc" ,gcc-7)
        ("autoconf" ,autoconf)
        ("automake" ,automake)
        ("libtool" ,libtool)
@@ -2344,6 +2345,9 @@ editors, IDEs, etc.")
      `(#:phases (modify-phases %standard-phases
                   (replace 'bootstrap
                     (lambda _
+                      ;; Work around GCC7 problem: <https://bugs.gnu.org/30756>.
+                      (for-each unsetenv '("C_INCLUDE_PATH" "CPLUS_INCLUDE_PATH"))
+
                       (setenv "NOCONFIGURE" "true")
                       (invoke "sh" "autogen.sh"))))))
   (synopsis "Enhanced VTE terminal widget")