Add pyAMReX_CCACHE Option (#247)

Cleaner way to disable CCache in package managers.

Author: ax3l

CMakeLists.txt

@@ -40,7 +40,15 @@ set_cxx17_superbuild()
 # this is an optional tool that stores compiled object files; allows fast
 # re-builds even with "make clean" in between. Mainly used to store AMReX
 # objects
-set_ccache()
+if(CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR)
+    set(pyAMReX_CCACHE_DEFAULT ON)
+else()
+    set(pyAMReX_CCACHE_DEFAULT OFF)  # we are a subproject in a superbuild
+endif()
+option(pyAMReX_CCACHE "Enable ccache for faster rebuilds" ${pyAMReX_CCACHE_DEFAULT})
+if(pyAMReX_CCACHE)
+    set_ccache()
+endif()
 
 
 # Output (build) Directories ##################################################

docs/source/install/cmake.rst

@@ -108,7 +108,7 @@ By default, the most important dependencies of pyAMReX are automatically downloa
 CMake Option                  Default & Values                               Description
 ============================= ============================================== ===========================================================
 ``BUILD_SHARED_LIBS``         ON/**OFF**                                     Build shared libraries for dependencies
-``CCACHE_PROGRAM``            First found ``ccache`` executable.             Set to ``-DCCACHE_PROGRAM=NO`` to disable CCache.
+``pyAMReX_CCACHE``            **ON**/OFF                                     Search and use CCache to speed up rebuilds.
 ``pyAMReX_amrex_src``         *None*                                         Path to AMReX source directory (preferred if set)
 ``pyAMReX_amrex_repo``        ``https://github.com/AMReX-Codes/amrex.git``   Repository URI to pull and build AMReX from
 ``pyAMReX_amrex_branch``      *we set and maintain a compatible commit*      Repository branch for ``pyAMReX_amrex_repo``