fix RTS linker compilation failure on Solaris

Reviewers: bgamari, austin

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1341

rts/Linker.c

@@ -78,7 +78,8 @@
     (   defined(linux_HOST_OS)     || defined(freebsd_HOST_OS) || \
         defined(dragonfly_HOST_OS) || defined(netbsd_HOST_OS ) || \
         defined(openbsd_HOST_OS  ) || defined(darwin_HOST_OS ) || \
-        defined(kfreebsdgnu_HOST_OS) || defined(gnu_HOST_OS)))
+        defined(kfreebsdgnu_HOST_OS) || defined(gnu_HOST_OS  ) || \
+        defined(solaris2_HOST_OS)))
 /* Don't use mmap on powerpc_HOST_ARCH as mmap doesn't support
  * reallocating but we need to allocate jump islands just after each
  * object images. Otherwise relative branches to jump islands can fail