Unconditionally include <string.h>, to avoid implicit function
declarations.  libXpm defines SYSV during the build, which is why they
do not see t his isssue.

diff --git a/lib/Xm/XpmI.h b/lib/Xm/XpmI.h
index bbba02b0cac1f91e..3468f2d1edf84f7c 100644
--- a/lib/Xm/XpmI.h
+++ b/lib/Xm/XpmI.h
@@ -118,9 +118,9 @@ extern "C" {
 extern FILE *popen();
 #endif
 
-#if defined(SYSV) || defined(SVR4) || defined(VMS) || defined(WIN32) || defined (_SVID_SOURCE)
 #include <string.h>
 
+#if defined(SYSV) || defined(SVR4) || defined(VMS) || defined(WIN32) || defined (_SVID_SOURCE)
 #ifndef index
 #define index strchr
 #endif