Enable ccache for lldb-(arm/aarch64)-ubuntu builders

This patch enables the use of ccache by LLDB ARM/AArch64 buildbots.
I have added following cmake switches to lldb-(arm/aarch64)-ubuntu
builders:
-DCMAKE_C_COMPILER_LAUNCHER=ccache
-DCMAKE_CXX_COMPILER_LAUNCHER=ccache
diff --git a/buildbot/osuosl/master/config/builders.py b/buildbot/osuosl/master/config/builders.py
index e32b61a..adb579a 100644
--- a/buildbot/osuosl/master/config/builders.py
+++ b/buildbot/osuosl/master/config/builders.py
@@ -962,6 +962,8 @@
                     extra_cmake_args=['-DLLVM_ENABLE_ASSERTIONS=True',
                                       '-DLLVM_LIT_ARGS="-svj 8"',
                                       '-DLLVM_USE_LINKER=gold',
+                                      '-DCMAKE_C_COMPILER_LAUNCHER=ccache',
+                                      '-DCMAKE_CXX_COMPILER_LAUNCHER=ccache',
                                       '-DCMAKE_C_COMPILER=clang',
                                       '-DCMAKE_CXX_COMPILER=clang++'])},
         {'name': "lldb-arm-ubuntu",
@@ -973,6 +975,8 @@
                     extra_cmake_args=['-DLLVM_ENABLE_ASSERTIONS=True',
                                       '-DLLVM_LIT_ARGS="-svj 8"',
                                       '-DLLVM_USE_LINKER=gold',
+                                      '-DCMAKE_C_COMPILER_LAUNCHER=ccache',
+                                      '-DCMAKE_CXX_COMPILER_LAUNCHER=ccache',
                                       '-DCMAKE_C_COMPILER=clang',
                                       '-DCMAKE_CXX_COMPILER=clang++'])},
         {'name': "lldb-x64-windows-ninja",