Disables Travis builds of C++ code with clang.

There is a compatibility issue with some versions of clang++ and some
C++ headers, related to the __float128 type, which causes builds to
fail.  Until this is reproducible outside Travis, it's best to disable
the C++ components when building with clang, rather than having the
test fail for reasons having nothing to do with GPSD itself.
Non-clang C++ builds are still tested as are non-C++ builds with
clang.

TESTED:
Script change to accept added options work.
Real test won't happen until this code is pushed.
Only Travis-related files are touched.

.travis.build

@@ -8,7 +8,7 @@ eval "$(dpkg-buildflags --export=sh)"
 
 export DEB_HOST_MULTIARCH=$(dpkg-architecture -qDEB_HOST_MULTIARCH)
 
-SCONSOPTS="prefix=/usr"
+SCONSOPTS="$@ prefix=/usr"
 SCONSOPTS="${SCONSOPTS} systemd=yes"
 SCONSOPTS="${SCONSOPTS} nostrip=yes"
 SCONSOPTS="${SCONSOPTS} dbus_export=yes"

.travis.yml

@@ -1,9 +1,13 @@
 sudo: required
 language: generic
 
+# Some versions of clang++ don't work with some C++ headers, due to an
+# issue with __float128.  Until this is reproducible in a more debuggable
+# context, we disable the C++ builds in the clang case.
+
 env:
     - TRAVIS_DEBIAN_DISTRIBUTION=unstable TRAVIS_DEBIAN_BUILD_COMMAND="/bin/bash .travis.build" TRAVIS_DEBIAN_BUILD_DEPENDENCIES="build-essential debhelper po-debconf python-all-dev python-all-dbg xsltproc docbook-xsl docbook-xml asciidoc libncurses-dev libusb-1.0-0-dev libdbus-1-dev libglib2.0-dev libdbus-glib-1-dev makedev libbluetooth-dev libqt4-dev lsb-release bc dpkg-dev scons chrpath dh-buildinfo pps-tools dh-systemd"
-    - TRAVIS_DEBIAN_DISTRIBUTION=unstable TRAVIS_DEBIAN_BUILD_COMMAND="/bin/bash .travis.build" TRAVIS_DEBIAN_BUILD_DEPENDENCIES="build-essential debhelper po-debconf python-all-dev python-all-dbg xsltproc docbook-xsl docbook-xml asciidoc libncurses-dev libusb-1.0-0-dev libdbus-1-dev libglib2.0-dev libdbus-glib-1-dev makedev libbluetooth-dev libqt4-dev lsb-release bc dpkg-dev scons chrpath dh-buildinfo pps-tools dh-systemd clang" TRAVIS_DEBIAN_BUILD_ENVIRONMENT="CC=clang CXX=clang++"
+    - TRAVIS_DEBIAN_DISTRIBUTION=unstable TRAVIS_DEBIAN_BUILD_COMMAND="/bin/bash .travis.build libgpsmm=no qt=no" TRAVIS_DEBIAN_BUILD_DEPENDENCIES="build-essential debhelper po-debconf python-all-dev python-all-dbg xsltproc docbook-xsl docbook-xml asciidoc libncurses-dev libusb-1.0-0-dev libdbus-1-dev libglib2.0-dev libdbus-glib-1-dev makedev libbluetooth-dev libqt4-dev lsb-release bc dpkg-dev scons chrpath dh-buildinfo pps-tools dh-systemd clang" TRAVIS_DEBIAN_BUILD_ENVIRONMENT="CC=clang CXX=clang++"
     - TRAVIS_DEBIAN_DISTRIBUTION=stable TRAVIS_DEBIAN_BUILD_COMMAND="/bin/bash .travis.build" TRAVIS_DEBIAN_BUILD_DEPENDENCIES="build-essential debhelper po-debconf python-all-dev python-all-dbg xsltproc docbook-xsl docbook-xml asciidoc libncurses-dev libusb-1.0-0-dev libdbus-1-dev libglib2.0-dev libdbus-glib-1-dev makedev libbluetooth-dev libqt4-dev lsb-release bc dpkg-dev scons chrpath dh-buildinfo pps-tools dh-systemd"
 
 services: