Use same flags to compile STM32F1 library as for whose examples

We use a compiler witch defaults to --with-fpu=fpv4-sp-d16. Therefor the STM32F1 library was compiled using this FPU support, but the examples for STM32F1 have the fpu set tosoft since  -msoft-float is used. When the library is compiled with that flag too, we can compile those examples.