Expose USE_VALGRIND compilation flag as use-valgrind feature

heed/Cargo.toml

@@ -110,6 +110,8 @@ mdb_idl_logn_16 = ["lmdb-master-sys/mdb_idl_logn_16"]
 # computers then you need to keep your keys within the smaller 1982 byte limit.
 longer-keys = ["lmdb-master-sys/longer-keys"]
 
+use-valgrind = ["lmdb-master-sys/use-valgrind"]
+
 [[example]]
 name = "rmp-serde"
 required-features = ["serde-rmp"]

lmdb-master-sys/Cargo.toml

@@ -60,6 +60,7 @@ mdb_idl_logn_13 = []
 mdb_idl_logn_14 = []
 mdb_idl_logn_15 = []
 mdb_idl_logn_16 = []
+use-valgrind = []
 
 # Setting this enables you to use keys longer than 511 bytes. The exact limit
 # is computed by LMDB at compile time. You can find the exact value by calling

lmdb-master-sys/build.rs

@@ -137,6 +137,10 @@ fn main() {
         builder.define("MDB_USE_POSIX_SEM", None);
     }
 
+    if cfg!(feature = "use-valgrind") {
+        builder.define("USE_VALGRIND", None);
+    }
+
     if cfg!(feature = "asan") {
         builder.flag("-fsanitize=address");
     }