add pkgconfig as dependence for flux packages (#11036)

var/spack/repos/builtin/packages/flux-core/package.py

@@ -48,6 +48,7 @@ class FluxCore(AutotoolsPackage):
     depends_on("py-pyyaml", type=('build', 'run'), when="@0.11.0:,master")
     depends_on("py-jsonschema", type=('build', 'run'), when="@master")
     depends_on("jansson")
+    depends_on("pkgconfig")
     depends_on("yaml-cpp", when="@:0.11.0")
     depends_on("lz4", when="@0.11.0:,master")
 

var/spack/repos/builtin/packages/flux-sched/package.py

@@ -31,6 +31,7 @@ class FluxSched(AutotoolsPackage):
     depends_on("libxml2@2.9.1:", when="@0.6.0,master")
     depends_on("yaml-cpp", when="@0.7.0:")
     depends_on("libuuid")
+    depends_on("pkgconfig")
 
     depends_on("flux-core", type=('build', 'link', 'run'))
     depends_on("flux-core+cuda", when='+cuda')