Fix clang ci

[guitorri]

No description provided.

[yodalee]

"configure: error: The qucs-core package requires an c++ compiler with namespace."
I got this error too
I'm using Archlinux as my OS

The problem is generated by qucs-core/m4/namespace.m4. I'm examine it now.

[yodalee]

Well that is funny. I test configure on my desktop, and it passes the namespace testing. Maybe because the version of tools, since I just upgrade my laptop to newest package.
Here is my desktop compile tool version list
autoconf 2.69-1
automake 1.14-1
binutils 2.23.2-3
bison 3.0.1-1
fakeroot 1.20-1
file 5.15-1
findutils 4.4.2-5
flex 2.5.37-1
gawk 4.1.0-2
gcc 4.8.2-4
gettext 0.18.3.1-2
grep 2.15-1
groff 1.22.2-5
gzip 1.6-1
libtool 2.4.2-12
m4 1.4.17-1
make 3.82-6
pacman 4.1.2-4
patch 2.7.1-2
pkg-config 0.28-1
sed 4.2.2-3
sudo 1.8.8-1
texinfo 5.2-2
util-linux 2.24-1
which 2.20-6

[guitorri]

Last time it worked with clang 3.3, see https://travis-ci.org/Qucs/qucs/jobs/22975514
It seems Travis updated to clang 3.4, that could be the source of the issue.
The failure happens during when configure tries to test link to Qt to define the library directory and when it tests for C++11 features such as namespaces. Without access to the logs it is hard to see what is going on. Maybe we should reach the Travis IRC to get help.

[guitorri]

I believe the issue is caused because the
AC_PROG_CXX(clang++ g++)
will define the x$GCC variable and prepend flags to CXXFLAGS that are unknown to Clang.
Reordering the compiler tests seem to eliminate the issue.
Testing now with clang3.3.

[yodalee]

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