Use clang 3.5 over 3.8

the llvm apt repo was removed and finding the exact rev of the llvm
toolchain that worked perfecting in our dockerfile is a problem.

We looked at the reasons why we were using this version of clang and it
appears to be this compiler warning.

`was built for newer OSX version (10.11) than being linked
(10.6)`

When you look at the dockerfile this makes sense.

```
ENV OSX_SDK MacOSX10.11.sdk
ENV OSX_CROSS_COMMIT 8aa9b71a394905e6c5f4b59e2b97b87a004658a4
RUN set -x \
	&& export OSXCROSS_PATH="/osxcross" \
	&& git clone https://github.com/tpoechtrager/osxcross.git $OSXCROSS_PATH \
	&& ( cd $OSXCROSS_PATH && git checkout -q $OSX_CROSS_COMMIT) \
	&& curl -sSL https://s3.dockerproject.org/darwin/v2/${OSX_SDK}.tar.xz -o "${OSXCROSS_PATH}/tarballs/${OSX_SDK}.tar.xz" \
	&& UNATTENDED=yes OSX_VERSION_MIN=10.6 ${OSXCROSS_PATH}/build.sh
ENV PATH /osxcross/target/bin:$PATH
```

We are basically using the 10.11 sdk but linking to 10.6 as the
min version so this warning should be expected.

Also the docs on the osxcross project require clan 3.2+, not 3.8.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>
(cherry picked from commit f8dacaf0ab7ca533cc3a33c6d06f7dca3e347955)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Dockerfile

@@ -30,10 +30,6 @@ RUN apt-key adv --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys E87
 	|| apt-key adv --keyserver hkp://pgp.mit.edu:80 --recv-keys E871F18B51E0147C77796AC81196BA81F6B0FC61
 RUN echo deb http://ppa.launchpad.net/zfs-native/stable/ubuntu trusty main > /etc/apt/sources.list.d/zfs.list
 
-# add llvm repo
-RUN apt-key adv --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys 6084F3CF814B57C1CF12EFD515CF4D18AF4F7421 \
-	|| apt-key adv --keyserver hkp://pgp.mit.edu:80 --recv-keys 6084F3CF814B57C1CF12EFD515CF4D18AF4F7421
-RUN echo deb http://llvm.org/apt/jessie/ llvm-toolchain-jessie-3.8 main > /etc/apt/sources.list.d/llvm.list
 
 # allow replacing httpredir mirror
 ARG APT_MIRROR=httpredir.debian.org
@@ -49,7 +45,7 @@ RUN apt-get update && apt-get install -y \
 	bsdmainutils \
 	btrfs-tools \
 	build-essential \
-	clang-3.8 \
+	clang \
 	createrepo \
 	curl \
 	dpkg-sig \
@@ -76,10 +72,7 @@ RUN apt-get update && apt-get install -y \
 	tar \
 	zip \
 	--no-install-recommends \
-	&& pip install awscli==1.10.15 \
-	&& ln -snf /usr/bin/clang-3.8 /usr/local/bin/clang \
-	&& ln -snf /usr/bin/clang++-3.8 /usr/local/bin/clang++
-
+	&& pip install awscli==1.10.15
 # Get lvm2 source for compiling statically
 ENV LVM2_VERSION 2.02.103
 RUN mkdir -p /usr/local/lvm2 \