include libsqlite3-sys optionally

Cargo.toml

@@ -14,7 +14,7 @@ build = "build.rs"
 # Empty to keep compatibility, prefer to set USE_SYSLOG=true
 enable_syslog = []
 mysql = ["diesel/mysql", "diesel_migrations/mysql"]
-sqlite = ["diesel/sqlite", "diesel_migrations/sqlite"]
+sqlite = ["diesel/sqlite", "diesel_migrations/sqlite", "libsqlite3-sys"]
 
 [target."cfg(not(windows))".dependencies]
 syslog = "4.0.1"
@@ -53,7 +53,7 @@ diesel = { version = "1.4.2", features = ["mysql", "sqlite", "chrono", "r2d2"] }
 diesel_migrations = { version = "1.4.0", features = ["mysql", "sqlite"] }
 
 # Bundled SQLite                                           
-libsqlite3-sys = { version = "0.12.0", features = ["bundled"] }
+libsqlite3-sys = { version = "0.12.0", features = ["bundled"], optional = true }
 
 # Crypto library
 ring = "0.14.6"