Get USBHost to build and run with GCC_ARM

[adamgreen]

I have made some changes to the USBHost code to get it building with GCC_ARM but I am not confident enough in the changes to issue a pull request. Instead, I would really appreciate a code review of the changes which can be viewed at the following link: https://github.com/adamgreen/mbed/compare/master...gccFixUSBHost The commit descriptions contain more details about each of my changes.

What I have done for testing so far:

• Made sure the library builds successfully with GCC_ARM using my makefiles and the official mbed python build scripts.
• Used GCC_ARM to build and test the USBHostMSD_HelloWorld sample found here-> http://mbed.org/handbook/USBHostMSD. It ran successfully.
• I took my updated USBHost library sources and uploaded then into a USBHostMSD_HelloWorld project on the mbed site. I then built the code using the online compiler and tested the resulting binary.
• I have used GCC_ARM to build and test USBHostMouse, USBHostKeyboard, USBHostSerial, and USBHostHub samples as found in the mbed Handbook.

Thanks and I look forward to your feedback.

-Adam

[adamgreen]

Opened pull request #67 to track my changes for this issue.