build(make): update arm/clang to latest versions

Update our testing framework to utilise Arm Compiler v6.18. On jenkins
and local runs, the LLVM toolchain is downloaded and its path prepended
to the PATH variable so that the host machine can find the latest tool
along with with its binutils.

Change-Id: Ie1c984ba01e3a8e0666e1e1f35b9303293b032cb
Signed-off-by: Harrison Mutai <harrison.mutai@arm.com>
diff --git a/script/tf-coverity/common-def.sh b/script/tf-coverity/common-def.sh
index 5d2cf13..82f391e 100644
--- a/script/tf-coverity/common-def.sh
+++ b/script/tf-coverity/common-def.sh
@@ -65,10 +65,11 @@
 
 # Provide correct armclang toolchain based on environment
 set_armclang_toolchain() {
-    local armclang_path="/home/buildslave/tools/armclang-6.8/bin"
+    # FIXME: ARMCompiler 6.18 is symlinked to 6.17 until it is available on OpenCI.
+    local armclang_path="/home/buildslave/tools/armclang-6.17/bin"
 
     # if under arm enviroment, overide cross-compilation path
-    is_arm_jenkins_env || upon "$local_ci" && armclang_path="/arm/warehouse/Distributions/FA/ARMCompiler/6.8/25/standalone-linux-x86_64-rel/bin"
+    is_arm_jenkins_env || upon "$local_ci" && armclang_path="/arm/warehouse/Distributions/FA/ARMCompiler/6.18/19/standalone-linux-x86_64-rel/bin"
 
     echo "${armclang_path}/armclang"
 }