rts: Check for program_invocation_short_name via autoconf

Instead of assuming support on all Linuxes.

configure.ac

@@ -918,6 +918,11 @@ AC_CHECK_DECLS([ctime_r], , ,
 #define _POSIX_C_SOURCE 199506L
 #include <time.h>])
 
+dnl On Linux we should have program_invocation_short_name
+AC_CHECK_DECLS([program_invocation_short_name], , ,
+[#define _GNU_SOURCE 1
+#include <errno.h>])
+
 dnl ** check for mingwex library
 AC_CHECK_LIB(
   [mingwex],

rts/Task.c

@@ -477,7 +477,7 @@ startWorkerTask (Capability *cap)
   // Set the name of the worker thread to the original process name followed by
   // ":w", but only if we're on Linux where the program_invocation_short_name
   // global is available.
-#if defined(linux_HOST_OS)
+#if defined(HAVE_PROGRAM_INVOCATION_SHORT_NAME)
   size_t procname_len = strlen(program_invocation_short_name);
   char worker_name[16];
   // The kernel only allocates 16 bytes for thread names, so we truncate if the