Build libsodium with ccache and fPIC

fPIC is needed in case we are building a shared liblokinet (within which
we want the static libsodium).

cmake/DownloadLibSodium.cmake

@@ -13,10 +13,13 @@ file(MAKE_DIRECTORY ${LIBSODIUM_PREFIX}/include)
 include(ExternalProject)
 include(ProcessorCount)
 
+set(sodium_cc ${CMAKE_C_COMPILER})
+if(CCACHE_PROGRAM)
+  set(sodium_cc "${CCACHE_PROGRAM} ${sodium_cc}")
+endif()
+set(SODIUM_CONFIGURE ./configure --prefix=${LIBSODIUM_PREFIX} --enable-static --disable-shared --with-pic --quiet CC=${sodium_cc})
 if (CMAKE_C_COMPILER_ARG1)
-  set(SODIUM_CONFIGURE ./configure --prefix=${LIBSODIUM_PREFIX} --enable-static --disable-shared CC=${CMAKE_C_COMPILER} CPPFLAGS=${CMAKE_C_COMPILER_ARG1})
-else()
-  set(SODIUM_CONFIGURE ./configure --prefix=${LIBSODIUM_PREFIX} --enable-static --disable-shared CC=${CMAKE_C_COMPILER})
+  set(SODIUM_CONFIGURE ${SODIUM_CONFIGURE} CPPFLAGS=${CMAKE_C_COMPILER_ARG1})
 endif()
 
 if (CROSS_TARGET)