[libxml2] autotools: Disable parallel Python build

[Nick Wellnhofer <nwellnhof src gnome org>]

commit ea8f7c92a9e3f7d89e57b0a1eae0229555da7356
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Tue Sep 6 00:47:00 2022 +0200

    autotools: Disable parallel Python build
    
    Makefile rules with multiple output files don't work reliably with
    parallel builds. There are several ways to fix this issue with GNU Make,
    but they aren't portable. I'd be really interested in a totally
    reliable, cross-platform solution to this problem.
    
    .NOTPARALLEL is also understood by BSD make, at least.

 python/Makefile.am | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/python/Makefile.am b/python/Makefile.am
index 778270df..07024346 100644
--- a/python/Makefile.am
+++ b/python/Makefile.am
@@ -1,5 +1,9 @@
 # Makefile for libxml2 python library
 
+# We use a rule with multiple output files which creates problems with
+# parallel builds.
+.NOTPARALLEL:
+
 SUBDIRS = . tests
 
 docsdir = $(docdir)/python