[PATCH] Makefile.am: filter -Wl,--no-undefined

[Fabrice Fontaine <fontaine.fabrice@gmail.com>]

Commit 1d14ef82f4a3be741bcdf6b1c6d51ce9dce43567 does not completely fix
the build with python 3.8 as we still get link failure due to
'-z undefs' being ignored by some versions of ld.

Indeed, -z undefs was added by commit
97a232d7335f3bd0231fd9cd39455bde1d563922 in upstream binutils, and this
commit was first present in binutils 2.30.
So any toolchain using binutils version older than that won't have
-z undefs and will build fail on:

/home/buildroot/autobuild/instance-0/output-1/host/opt/ext-toolchain/bin/../lib/gcc/mips-linux-gnu/5.3.0/../../../../mips-linux-gnu/bin/ld: warning: -z undefs ignored.

/home/naourr/work/instance-1/output-1/host/opt/ext-toolchain/bin/../lib/gcc/aarch64_be-linux-gnu/7.3.1/../../../../aarch64_be-linux-gnu/bin/ld: warning: -z undefs ignored.

So filter -Wl,--no-undefined to fix the issue

Fixes:
 - http://autobuild.buildroot.org/results/e9645d9969481b09f507f6e0d0b35faaa283eb60
 - http://autobuild.buildroot.org/results/06a6d865b6b7d8ebd793bde214f4a4c40e0962e1

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
---
 Makefile.am | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/Makefile.am b/Makefile.am
index 8e9c90d..47505c1 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -173,7 +173,10 @@ CPYTHON_MODULE_CFLAGS = \
 	$(AM_CFLAGS) -DCPYTHON_COMPILING_IN_PYPY=0 \
 	$(PYTHON_NOWARN) $(PYTHON_CFLAGS) \
 	-fvisibility=default
-CPYTHON_MODULE_LDFLAGS = $(AM_LDFLAGS) -module -avoid-version -shared -Wl,-z,undefs
+# Filter -Wl,--no-undefined to fix build with python 3.8
+comma = ,
+CPYTHON_MODULE_LDFLAGS = $(subst -Wl$(comma)--no-undefined,,$(AM_LDFLAGS))
+CPYTHON_MODULE_LDFLAGS += -module -avoid-version -shared
 
 if BUILD_PYTHON
 pkgpyexec_LTLIBRARIES = \
-- 
2.24.0