BaseTools: fix spec keyword parsing

[Ashwin-Veeraiah]

Fixes SPEC keyword parsing to match EDK2 specification

Description

When SPEC keyword is used in the INF file, it does not create the equivalent #define in the autogen.h file of the module. Additionally it creates a line in autogenerated makefile. This generated line will cause builds to break of we follow the specification as defined in the example here, [https://github.com/tianocore-docs/edk2-InfSpecification/blob/master/3_edk_ii_inf_file_format/34_%5Bdefines%5D_section.md] Ex : SPEC USB_SPECIFICATION_VERSION = 2.0 The changes fixes the autogen code to function as mentioned by the documentation.

• [ ] Breaking change?
  • Breaking change - Does this PR cause a break in build or boot behavior?
  • N/A
• [ ] Impacts security?
  • Security - Does this PR have a direct security impact?
  • N/A
• [ ] Includes tests?
  • Tests - Does this PR include any explicit test code?
  • N/A

How This Was Tested

Tested locally with builds.

Integration Instructions

N/A

[mergify[bot]]

PR can not be merged due to conflict. Please rebase and resubmit