add force-engine feature for enabling engine module (alexcrichton#151)

* add force-engine feature for enabling engine module

* add the feature flag to Cargo.toml

Author: Kyle Criddle

Cargo.toml

@@ -31,6 +31,8 @@ idea = []
 # Enables compilation of SEED, a symmetric key block cypher mostly used in South Korea, but
 # otherwise not widely supported.
 seed = []
+# Forces configuring Engine module support.
+force-engine = []
 
 [workspace]
 members = ['testcrate']

src/lib.rs

@@ -185,10 +185,13 @@ impl Build {
         }
 
         if target.contains("musl") || target.contains("windows") {
-            // This actually fails to compile on musl (it needs linux/version.h
+            // Engine module fails to compile on musl (it needs linux/version.h
             // right now) but we don't actually need this most of the time.
             // API of engine.c ld fail in Windows.
-            configure.arg("no-engine");
+            // Disable engine module unless force-engine feature specified
+            if !cfg!(feature = "force-engine") {
+                configure.arg("no-engine");
+            }
         }
 
         if target.contains("musl") {