Allow VECT_TAB_OFFSET to be overridden externally

[pieterconradie]

This patch allows the VECT_TAB_OFFSET #define to be overridden by the IDE or Makefile without manually editing the system_stm32l0xx.c file. It is useful if the application must be compiled for debugging (no vector table offset) or for release (vector table offset to accommodate a bootloader).

IMPORTANT INFORMATION

Contributor License Agreement (CLA)

• The Pull Request feature will be considered by STMicroelectronics after the signature of a Contributor License Agreement (CLA) by the submitter.
• If you did not sign such agreement, please follow the steps mentioned in the CONTRIBUTING.md file.

[ST-dot-com]

This pull request has been refused, the Contribution License Agreement must be signed.