pkgconfig: add conflict for PGI (#18236)

var/spack/repos/builtin/packages/pkg-config/package.py

@@ -25,6 +25,9 @@ class PkgConfig(AutotoolsPackage):
     # The following patch is needed for gcc-6.1
     patch('g_date_strftime.patch', when='@:0.29.1')
 
+    # https://github.com/spack/spack/issues/3525
+    conflicts('%pgi')
+
     parallel = False
 
     executables = ['^pkg-config$']

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

@@ -31,6 +31,9 @@ class Pkgconf(AutotoolsPackage):
     # TODO: Add a package for the kyua testing framework
     # depends_on('kyua', type='test')
 
+    # https://github.com/spack/spack/issues/3525
+    conflicts('%pgi')
+
     executables = ['^pkgconf$', '^pkg-config$']
 
     @classmethod