Ensure all exported paths use Posix style separators.
Ensure all exported paths use Posix style separators.

mbed_config.h is a file that is placed in your project root when you
export. This allows the configuration to be used by your IDE. When this
file already exists (due to a previous export), it changed the compiler
include option on Windows from "-include mbed_config.h" to "-include
.\mbed_config.h". The "\" character was interpreted as an escape
character "\m" and broke the build. This converts all resource paths to
use the Posix path separator "/" before writing project files to avoid
this issue.

kjbracey-arm/mbed,mbedmicro/mbed,kjbracey-arm/mbed,andcor02/mbed-os,andcor02/mbed-os,mbedmicro/mbed,mbedmicro/mbed,andcor02/mbed-os,kjbracey-arm/mbed,mbedmicro/mbed,andcor02/mbed-os,andcor02/mbed-os,kjbracey-arm/mbed,andcor02/mbed-os,mbedmicro/mbed