libtirpc: Fix directories returned for header files (#23332)

libtirpc puts its header files under prefix/include/tirpc, but
spack was returning just prefix/include for location of headers.

This will cause spack to return both prefix/include and
prefix/include/tirpc for headers, so both

include <rpc/xdr.h>

or

include <tirpc/rpc/xdr.h>

should work.

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

@@ -23,3 +23,13 @@ class Libtirpc(AutotoolsPackage):
     # FIXME: build error on macOS
     # auth_none.c:81:9: error: unknown type name 'mutex_t'
     conflicts('platform=darwin', msg='Does not build on macOS')
+
+    @property
+    def headers(self):
+        hdrs = find_all_headers(self.prefix.include)
+        # libtirpc puts headers under include/tirpc, but some codes (e.g. hdf)
+        # do not expect a tirpc component.  Since some might, we return
+        # both prefix.include.tirpc and prefix.include as header paths
+        if hdrs:
+            hdrs.directories = [self.prefix.include.tirpc, self.prefix.include]
+        return hdrs or None