Workaround bug with old distributions c99 issue

When in c99 mode (which is needed for some of our newer additions),
old distributions has an glibc inlining bug which triggers lots of
duplicated symbols.

Add a cabal flag to revert the inliner to c89 mode.

Fixes #64

cryptonite.cabal

@@ -80,6 +80,11 @@ Flag support_deepseq
   Default:           True
   Manual:            True
 
+Flag old_toolchain_inliner
+  Description:       use -fgnu89-inline to workaround an old compiler / linker / glibc issue.
+  Default:           False
+  Manual:            True
+
 Library
   Exposed-modules:   Crypto.Cipher.AES
                      Crypto.Cipher.Blowfish
@@ -187,6 +192,8 @@ Library
   ghc-options:       -Wall -fwarn-tabs -optc-O3 -fno-warn-unused-imports
   default-language:  Haskell2010
   cc-options:        -std=gnu99
+  if flag(old_toolchain_inliner)
+    cc-options:      -fgnu89-inline
   C-sources:         cbits/cryptonite_chacha.c
                    , cbits/cryptonite_salsa.c
                    , cbits/cryptonite_rc4.c