ci: add ccache to clang builds

Tools/scripts/build_ci.sh

@@ -19,6 +19,10 @@ export NUTTX_GIT_VERSION="ci_test"
 export PX4_GIT_VERSION="ci_test"
 export CCACHE_SLOPPINESS="include_file_ctime,include_file_mtime"
 
+if [[ "$cxx_compiler" == "clang++" ]]; then
+  export CCACHE_CPP2="true"
+fi
+
 # If CI_BUILD_TARGET is not set, default to all of them
 if [ -z "$CI_BUILD_TARGET" ]; then
     CI_BUILD_TARGET="sitl linux navio raspilot minlure bebop px4-v2 px4-v4"

Tools/scripts/configure-ci.sh

@@ -61,6 +61,8 @@ ln -s ~/opt/$CCACHE_ROOT/ccache ~/ccache/arm-none-eabi-g++
 ln -s ~/opt/$CCACHE_ROOT/ccache ~/ccache/arm-none-eabi-gcc
 ln -s ~/opt/$CCACHE_ROOT/ccache ~/ccache/arm-linux-gnueabihf-g++
 ln -s ~/opt/$CCACHE_ROOT/ccache ~/ccache/arm-linux-gnueabihf-gcc
+ln -s ~/opt/$CCACHE_ROOT/ccache ~/ccache/clang++
+ln -s ~/opt/$CCACHE_ROOT/ccache ~/ccache/clang
 
 exportline="export PATH=$HOME/ccache"
 exportline="${exportline}:$HOME/bin"