Add StackCheckLib Instances to Platform DSC Files (#198)

## Description

An instance of StackCheckLib must be in each DSC to accommodate
-fstack-protector and /GS flags.

- [x] Impacts functionality?
- **Functionality** - Does the change ultimately impact how firmware
functions?
- Examples: Add a new library, publish a new PPI, update an algorithm,
...
- [ ] Impacts security?
- **Security** - Does the change have a direct security impact on an
application,
    flow, or firmware?
  - Examples: Crypto algorithm change, buffer overflow fix, parameter
    validation improvement, ...
- [ ] Breaking change?
- **Breaking change** - Will anyone consuming this change experience a
break
    in build or boot behavior?
- Examples: Add a new library class, move a module to a different repo,
call
    a function in a new library class in a pre-existing module, ...
- [ ] Includes tests?
  - **Tests** - Does the change include any explicit test code?
  - Examples: Unit tests, integration tests, robot tests, ...
- [ ] Includes documentation?
- **Documentation** - Does the change contain explicit documentation
additions
    outside direct code modifications (and comments)?
- Examples: Update readme file, add feature readme file, link to
documentation
    on an a separate Web page, ...

## How This Was Tested

Tested in pipelines

## Integration Instructions

N/A

OemPkg/OemPkg.dsc

@@ -33,6 +33,7 @@
   PcdLib|MdePkg/Library/BasePcdLibNull/BasePcdLibNull.inf
   ReportStatusCodeLib|MdePkg/Library/BaseReportStatusCodeLibNull/BaseReportStatusCodeLibNull.inf
   UefiApplicationEntryPoint|MdePkg/Library/UefiApplicationEntryPoint/UefiApplicationEntryPoint.inf
+  NULL|MdePkg/Library/StackCheckLibNull/StackCheckLibNull.inf
 
   PrintLib|MdePkg/Library/BasePrintLib/BasePrintLib.inf
   HiiLib|MdeModulePkg/Library/UefiHiiLib/UefiHiiLib.inf