build: disable clang support in ci

- Disable clang test for travis and drone.io
- Add document about compiler requirement

Change-Id: I81f8dc31088d40f315dd4ec062bed5df8ab7b633
Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>

.drone.yml

@@ -19,50 +19,6 @@ steps:
   - if [ -n "$AS" ]; then $AS --version; fi
   - ./tools/test_autorun.sh "$TEST_TYPE"
 
----
-kind: pipeline
-name: arm64-linux-clang-3.8
-
-platform:
-  os: linux
-  arch: arm64
-
-steps:
-- name: arm64-linux-clang-3.8
-  image: ubuntu:xenial
-  environment:
-    C_COMPILER: clang
-  commands:
-  - if [ -n "$C_COMPILER" ]; then export CC="$C_COMPILER"; fi
-  - if [ -n "$AS_ASSEMBL" ]; then export AS="$AS_ASSEMBL"; fi
-  - apt-get -qq update
-  - apt-get install -qq -y build-essential clang git indent libtool libz-dev yasm autoconf
-  - if [ -n "$CC" ]; then $CC --version; fi
-  - if [ -n "$AS" ]; then $AS --version; fi
-  - ./tools/test_autorun.sh "$TEST_TYPE"
-
----
-kind: pipeline
-name: arm64-linux-clang-4.0
-
-platform:
-  os: linux
-  arch: arm64
-
-steps:
-- name: arm64-linux-clang-4.0
-  image: ubuntu:xenial
-  environment:
-    C_COMPILER: clang-4.0
-  commands:
-  - if [ -n "$C_COMPILER" ]; then export CC="$C_COMPILER"; fi
-  - if [ -n "$AS_ASSEMBL" ]; then export AS="$AS_ASSEMBL"; fi
-  - apt-get -qq update
-  - apt-get install -qq -y build-essential clang-4.0 git indent libtool libz-dev yasm autoconf
-  - if [ -n "$CC" ]; then $CC --version; fi
-  - if [ -n "$AS" ]; then $AS --version; fi
-  - ./tools/test_autorun.sh "$TEST_TYPE"
-
 ---
 kind: pipeline
 name: arm64-linux-gcc-4.7

.travis.yml

@@ -59,19 +59,13 @@ matrix:
             - g++-6
       env: C_COMPILER=gcc-6
 
-    ### arm64: clang-3.8
-    - os: linux
-      dist: xenial
-      arch: arm64
-      env: C_COMPILER=clang
-
     ### arm64: gcc-5.4
     - os: linux
       dist: xenial
       arch: arm64
       env: C_COMPILER=gcc
 
-    ### arm64: gcc-5.4
+    ### arm64: gcc-5.4 extended tests
     - os: linux
       dist: xenial
       arch: arm64

Build_For_Arm64.md

@@ -0,0 +1,35 @@
+Building ISA-L on Arm
+=================================================
+
+## Prerequisites
+
+* HOST CPU MUST be aarch64
+* Assembler: gas v2.24 or later
+* Compiler: gcc v4.7 or later
+* Make: GNU 'make'
+* Optional:
+  * Building with autotools requires autoconf/automake packages.
+
+## Autotools
+
+To build and install the library with autotools it is usually sufficient to run:
+
+    ./autogen.sh
+    ./configure
+    make
+    sudo make install
+
+## Makefile
+To use a standard makefile run:
+
+    make -f Makefile.unx
+
+
+### Other make targets
+Other targets include:
+* `make check` : create and run tests
+* `make tests` : create additional unit tests
+* `make perfs` : create included performance tests
+* `make ex`    : build examples
+* `make other` : build other utilities such as compression file tests
+* `make doc`   : build API manual