PrGate.yml: Add extra_pre_build_steps param (#378)

Adds a new template parameter called `extra_pre_build_steps` that allows
a step list to run before any stuart build related commands are
executed.

Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>

Author: makubacki

Jobs/PrGate.yml

@@ -41,6 +41,10 @@ parameters:
   displayName: Extra Build Command Arguments
   type: string
   default: 'CODE_COVERAGE=TRUE CC_FLATTEN=TRUE CC_FULL=TRUE'
+- name: extra_pre_build_steps
+  displayName: Extra Pre-Build Steps
+  type: stepList
+  default: []
 - name: extra_post_build_steps
   displayName: Extra Post-Build Steps
   type: stepList
@@ -166,6 +170,7 @@ jobs:
         tool_chain_tag: ${{ parameters.tool_chain_tag }}
         install_tools: ${{ and(not(eq(item.Value.SelfHostAgent, true)), not(parameters.container_build)) }}
         extra_install_step: ${{ parameters.extra_install_step }}
+        extra_pre_build_steps: ${{ parameters.extra_pre_build_steps }}
         extra_post_build_steps: ${{ parameters.extra_post_build_steps }}
         # This is to handle the matrices that do not specify this.
         ${{ if eq(item.Value.SelfHostAgent, true) }}:

Steps/PrGate.yml

@@ -64,6 +64,10 @@ parameters:
   displayName: Extra Install Steps
   type: stepList
   default: []
+- name: extra_pre_build_steps
+  displayName: Extra Pre-Build Steps
+  type: stepList
+  default: []
 - name: extra_post_build_steps
   displayName: Extra Post-Build Steps
   type: stepList
@@ -140,6 +144,9 @@ steps:
 - ${{ if eq(parameters.install_tools, true) }}:
   - template: InstallCoverageTools.yml
 
+# Potential pre-build steps
+- ${{ parameters.extra_pre_build_steps }}
+
 # Build repo
 - ${{ if eq(parameters.do_ci_setup, true) }}:
   - task: CmdLine@2