build: Conditional enabling of osx-private-key-storage compilation

Makefile.am now contains a condition to enable/disable compilation of
osx-private-key-storage, instead of relying on define in the key storage
implementation.

Change-Id: I4a2079d99cd515c744cbe8f90a34a39e5c8197fa
diff --git a/configure.ac b/configure.ac
index c668f29..5e19152 100644
--- a/configure.ac
+++ b/configure.ac
@@ -114,11 +114,13 @@
 ], [
     AC_MSG_RESULT([yes])
     AC_DEFINE_UNQUOTED([HAVE_OSX_SECURITY], 1, [1 if have the OSX framework.])
+    AM_CONDITIONAL(HAVE_OSX_SECURITY, true)
 
     OSX_SECURITY_LIBS="-framework Security"
     AC_SUBST([OSX_SECURITY_LIBS])
 ], [
     AC_MSG_RESULT([no])
+    AM_CONDITIONAL(HAVE_OSX_SECURITY, false)
 ])
 
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