* Change some cmake output to DEBUG level
Make SDK build more consistent with other libraries (use an INTERFACE marker library for inclusion tests)
Add PICO_SDK_PRE_LIST_FILES, PICO_SDK_POST_LIST_FILES build vars
* fix typo
* remove leftover debugging message
* pico_stdio_usb: be more explicit about includes, fix warning (#257)
* pico_base: NDEBUG backwards for absolute_time_t (#255)
* pico_util: missing extern C in queue.h (#249)
* build: remove -march which was masking -mcpu, now SVC available (#253)