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 b/configure
index 4e4f9e3..c01dfe0 100755
--- a/configure
+++ b/configure
@@ -8551,7 +8551,7 @@
 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="\$(BINLIBDEST)/config/ld_so_aix \$(CC) -bI:\$(BINLIBDEST)/config/python.exp"
 		;;
 	BeOS*)