Make set_drops_artifact_from_ir non-const.

Setters should be non-const but set_drops_artifact_from_ir isn't.
This patch fixes this.

This reason this didn't cause a compilation failure is that const
shared_ptr<X> is equivalent to X *const, not const X*.

Note that resolving the apparent const-safety issue will require
std::experimental::propagate_const or similar.

	* include/abg-suppression.h
	(suppression_base::set_drops_artifact_from_ir):
	Drop const qualifier.
	* src/abg-suppression.cc
	(suppression_base::set_drops_artifact_from_ir):
	Drop const qualifier.

Reviewed-by: Matthias Maennich <maennich@google.com>
Signed-off-by: Giuliano Procida <gprocida@google.com>
diff --git a/include/abg-suppression.h b/include/abg-suppression.h
index 4f1fb41..6383b93 100644
--- a/include/abg-suppression.h
+++ b/include/abg-suppression.h
@@ -71,7 +71,7 @@
   get_drops_artifact_from_ir() const;
 
   void
-  set_drops_artifact_from_ir(bool) const;
+  set_drops_artifact_from_ir(bool);
 
   bool
   get_is_artificial() const;
diff --git a/src/abg-suppression.cc b/src/abg-suppression.cc
index 41827dc..46e9563 100644
--- a/src/abg-suppression.cc
+++ b/src/abg-suppression.cc
@@ -97,7 +97,7 @@
 /// specification is to avoid adding the matched ABI artifact to the
 /// internal representation.
 void
-suppression_base::set_drops_artifact_from_ir(bool f) const
+suppression_base::set_drops_artifact_from_ir(bool f)
 {priv_->drops_artifact_ = f;}
 
 /// Test is the suppression specification is artificial.