Ask libtool to stop hiding some errors

For #13083, curiously, it did not print the actual error, just
that the compile failed with "Error 1".

In theory, this flag should cause it to report errors twice sometimes.
In practice, I'm pretty okay with reporting some twice if it avoids
reporting some never.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Damian Szuberski <szuberskidamian@gmail.com>
Signed-off-by: Rich Ercolani <rincebrain@gmail.com>
Closes #13086

lib/libtpool/Makefile.am

@@ -1,9 +1,13 @@
 include $(top_srcdir)/config/Rules.am
 
 AM_CFLAGS += -fvisibility=hidden
+
 # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61118
 AM_CFLAGS += $(NO_CLOBBERED)
 
+# See https://debbugs.gnu.org/cgi/bugreport.cgi?bug=54020
+AM_CFLAGS += -no-suppress
+
 noinst_LTLIBRARIES = libtpool.la
 
 USER_C = \