Fix pkg-config dependencies (#9738)

Replace dependencies on specific pkgconfig implementation (e.g. pkgconf)
with dependency on pkgconfig virtual package

var/spack/repos/builtin/packages/axel/package.py

@@ -18,6 +18,6 @@ class Axel(AutotoolsPackage):
     depends_on('autoconf', type='build')
     depends_on('automake', type='build')
     depends_on('libtool', type='build')
-    depends_on('pkgconf', type='build')
+    depends_on('pkgconfig', type='build')
     depends_on('gettext')
     depends_on('openssl')

var/spack/repos/builtin/packages/mscgen/package.py

@@ -19,5 +19,5 @@ class Mscgen(AutotoolsPackage):
 
     depends_on('flex')
     depends_on('bison')
-    depends_on('pkgconf')
+    depends_on('pkgconfig')
     depends_on('libgd')

var/spack/repos/builtin/packages/py-pyarrow/package.py

@@ -21,7 +21,7 @@ class PyPyarrow(PythonPackage):
     variant('parquet', default=False, description="Build with Parquet support")
 
     depends_on('cmake@3.0.0:', type='build')
-    depends_on('pkg-config', type='build')
+    depends_on('pkgconfig', type='build')
     depends_on('py-setuptools', type='build')
     depends_on('py-cython', type='build')
 

var/spack/repos/builtin/packages/unifycr/package.py

@@ -35,7 +35,7 @@ class Unifycr(AutotoolsPackage):
     depends_on('gotcha@0.0.2')
     depends_on('leveldb')
     depends_on('mpi')
-    depends_on('pkg-config@0.9.0:')
+    depends_on('pkgconfig')
 
     # Optional dependencies