Add configure checks for strdup

This adds the appropriate preprocessor macros for locating strdup
on older systems like the manylinux1 builder (see !99).
12 jobs for strdup-configure in 30 minutes and 17 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Level0
passed #31710
level0:lal

00:05:11

 
  Level1
passed #31711
level1:lalframe

00:02:34

passed #31712
level1:lalmetaio

00:02:22

passed #31713
level1:lalsimulation

00:05:44

passed #31714
level1:lalxml

00:02:13

 
  Level2
passed #31715
level2:lalburst

00:02:46

passed #31716
level2:lalinspiral

00:05:41

passed #31717
level2:lalpulsar

00:04:11

passed #31718
level2:lalstochastic

00:02:32

 
  Level3
passed #31719
level3:laldetchar

00:02:27

passed #31720
level3:lalinference

00:07:08

 
  Level4
passed #31721
level4:lalapps

00:06:29