Restore top-level .gitignore; testbuild.sh must distinguish CONFIG_ARM_TOOLCHAIN_GNU from other symbols that begin with the same string

Olimex-STM32_H407: Move board initialization logic from stm32_appinit.c to stm32_bringup.c; Add support for the RTC driver

Olimex-STM32-H407:  Pick up a few changes from PR38.  Most of those changes are, however, not appropriate or not incompliance with NuttX naming or coding style.

STM3240G-EVAL and VIEWTOOL-STM32F107: Refresh configurations; add support to register the RTC driver