.travis.yml: minor facelift

Apparently trusty image has newer clang, there is no need to pull
clang-3.9 packages. It's clang-5.0.0, installation is a bit quirky,
as it fails to compile for example strcmp(s,"-") without warning,
and complains about unreferred -I flags. But it's argued that benefits
of exercising newer sanitizer outweights the inconvenience of
additional -D__NO_STRING_INLINE and -Wno-unused-command-line-argument.

Also pull golang when actually needed.
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6185)

.travis.yml

@@ -16,12 +16,6 @@ before_install:
           git submodule update --init --recursive;
       fi;
 
-addons:
-    apt:
-        packages:
-            - ccache
-            - golang-1.6
-
 os:
     - linux
     - osx
@@ -48,8 +42,8 @@ matrix:
           compiler: gcc-5
           env: CONFIG_OPTS="--strict-warnings" COMMENT="Move to the BORINGTEST build when interoperable"
         - os: linux
-          compiler: clang-3.9
-          env: CONFIG_OPTS="--strict-warnings no-deprecated" BUILDONLY="yes"
+          compiler: clang
+          env: CONFIG_OPTS="--strict-warnings -D__NO_STRING_INLINES no-deprecated" BUILDONLY="yes"
         - os: linux
           addons:
               apt:
@@ -64,6 +58,7 @@ matrix:
                   packages:
                       - gcc-5
                       - g++-5
+                      - golang-1.6
                   sources:
                       - ubuntu-toolchain-r-test
           compiler: gcc-5
@@ -74,19 +69,20 @@ matrix:
                   packages:
                       - gcc-5
                       - g++-5
+                      - golang-1.6
                   sources:
                       - ubuntu-toolchain-r-test
           compiler: gcc-5
           env:  EXTENDED_TEST="yes" CONFIG_OPTS="--debug enable-ssl3 enable-ssl3-method enable-weak-ssl-ciphers enable-external-tests" BORINGSSL_TESTS="yes" CXX="g++-5" TESTS=95
         - os: linux
-          compiler: clang-3.9
-          env: EXTENDED_TEST="yes" CONFIG_OPTS="enable-msan"
+          compiler: clang
+          env: EXTENDED_TEST="yes" CONFIG_OPTS="enable-msan -D__NO_STRING_INLINES -Wno-unused-command-line-argument"
         - os: linux
-          compiler: clang-3.9
-          env:  EXTENDED_TEST="yes" CONFIG_OPTS="no-asm enable-ubsan enable-rc5 enable-md2 enable-ssl3 enable-ssl3-method enable-nextprotoneg -fno-sanitize=alignment no-shared -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION"
+          compiler: clang
+          env:  EXTENDED_TEST="yes" CONFIG_OPTS="no-asm enable-ubsan enable-rc5 enable-md2 enable-ssl3 enable-ssl3-method enable-nextprotoneg no-shared -fno-sanitize=alignment -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION -D__NO_STRING_INLINES -Wno-unused-command-line-argument"
         - os: linux
-          compiler: clang-3.9
-          env: EXTENDED_TEST="yes" CONFIG_OPTS="no-asm enable-asan enable-rc5 enable-md2 no-shared -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION"
+          compiler: clang
+          env: EXTENDED_TEST="yes" CONFIG_OPTS="no-asm enable-asan enable-rc5 enable-md2 no-shared -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION -D__NO_STRING_INLINES -Wno-unused-command-line-argument"
         - os: linux
           addons:
               apt: