Issue #10656: Fix out-of-tree building on AIX

The ld_so_aix script and python.exp file are created in the build directory.
Patch by Tristan Carel and Michael Haubenwallner.
diff --git a/configure.ac b/configure.ac
index 4e55871..0886b6e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2358,7 +2358,7 @@
 then
 	case $ac_sys_system/$ac_sys_release in
 	AIX*)
-		BLDSHARED="\$(srcdir)/Modules/ld_so_aix \$(CC) -bI:\$(srcdir)/Modules/python.exp"
+		BLDSHARED="Modules/ld_so_aix \$(CC) -bI:Modules/python.exp"
 		LDSHARED="\$(LIBPL)/ld_so_aix \$(CC) -bI:\$(LIBPL)/python.exp"
 		;;
 	IRIX/5*) LDSHARED="ld -shared";;