ci: Enable custom CXX flags, enable -Werror

- Add a new boolean to make and ninja builds (uhdAllowWarnings). It
  defaults to false.
- When asserted, we set build flags for make and ninja to

    -Werror -Wno-error=maybe-uninitialized

- Add a new parameter to make and ninja builds (uhdCxxFlags). It is
  currently unused

.ci/templates/steps-build-uhd-make.yml

@@ -6,6 +6,12 @@ parameters:
 - name: uhdEnableTraceLog
   type: boolean
   default: false
+- name: uhdAllowWarnings
+  type: boolean
+  default: false
+- name: uhdCxxFlags
+  type: string
+  default: ""
 
 steps:
 - script: |
@@ -15,6 +21,11 @@ steps:
       echo "Enabling UHD Tracing"
       export UHD_CI_CMAKE_OPTIONS="-DUHD_LOG_MIN_LEVEL=trace $UHD_CI_CMAKE_OPTIONS"
     fi
+    if [[ "${{ parameters.uhdAllowWarnings }}" = "False" ]]; then
+      echo "Warnings not allowed for this build."
+      export CXXFLAGS="-Werror -Wno-error=maybe-uninitialized $CXXFLAGS"
+    fi
+    export CXXFLAGS="${{ parameters.uhdCxxFlags }} $CXXFLAGS"
     cmake \
       $UHD_CI_CMAKE_OPTIONS \
       ${{ parameters.uhdSrcDir }}/host

.ci/templates/steps-build-uhd-ninja.yml

@@ -3,11 +3,22 @@ parameters:
   type: string
 - name: uhdBuildDir
   type: string
+- name: uhdAllowWarnings
+  type: boolean
+  default: false
+- name: uhdCxxFlags
+  type: string
+  default: ""
 
 steps:
 - script: |
     mkdir -p ${{ parameters.uhdBuildDir }}
     cd ${{ parameters.uhdBuildDir }}
+    if [[ "${{ parameters.uhdAllowWarnings }}" = "False" ]]; then
+      echo "Warnings not allowed for this build."
+      export CXXFLAGS="-Werror -Wno-error=maybe-uninitialized $CXXFLAGS"
+    fi
+    export CXXFLAGS="${{ parameters.uhdCxxFlags }} $CXXFLAGS"
     cmake -G Ninja ${{ parameters.uhdSrcDir }}/host
   displayName: cmake ninja UHD
 - script: |

.ci/uhd-pipeline.yml

@@ -11,8 +11,10 @@ trigger:
   paths:
     include:
     - host
-    - .ci/uhd-pipeline.yml
+    - .ci/
     - images/manifest.txt
+    exclude:
+    - .ci/docker
 pr:
   branches:
     include: