Set MAKEFLAGS to CARGO_MAKEFLAGS for the make command

Author: Eijebong

build.rs

@@ -35,6 +35,7 @@ fn main() {
     }
 
     let result = Command::new(make)
+        .env("MAKEFLAGS", env::var("CARGO_MAKEFLAGS").unwrap_or_default())
         .args(&["-R", "-f", "makefile.cargo"])
         .stdout(Stdio::inherit())
         .stderr(Stdio::inherit())

makefile.cargo

@@ -126,7 +126,7 @@ SRC_DIR = $(shell pwd)
 .PHONY : all maybe-configure
 
 all: maybe-configure
-	cd $(OUT_DIR) && $(MAKE) -f Makefile -j$(NUM_JOBS)
+	cd $(OUT_DIR) && $(MAKE) -f Makefile
 
 # Only touch and run configure if we need to, to avoid unnecessary rebuilds.
 # The second two time checks handle the case of configure.in and configure having