Update C example

.gitignore

@@ -25,4 +25,4 @@ Carthage
 # local stuff
 data/
 glean-core/data
-glean_app
+glean_app*

glean-core/ffi/examples/Makefile

@@ -1,12 +1,24 @@
-objects = glean_app.c $(wildcard ../../../target/release/libglean_ffi.so) $(wildcard ../../../target/release/libglean_ffi.dylib)
-headers = glean.h
+SRC = glean_app.c
+HEADERS = glean.h
 
-glean_app: $(objects) $(headers)
-	$(CC) $(CFLAGS) -o $@ $(objects)
+UNAME_S := $(shell uname -s)
+ifeq ($(UNAME_S),Linux)
+    OBJECTS_RELEASE = ../../../target/release/libglean_ffi.so
+    OBJECTS_DEBUG = ../../../target/debug/libglean_ffi.so
+endif
+ifeq ($(UNAME_S),Darwin)
+    OBJECTS_RELEASE = ../../../target/release/libglean_ffi.dylib
+    OBJECTS_DEBUG = ../../../target/debug/libglean_ffi.dylib
+endif
 
+glean_app: $(SRC) $(OBJECTS_DEBUG) $(HEADERS)
+	$(CC) $(CFLAGS) -o $@ $(SRC) $(OBJECTS_DEBUG)
 
-../../../target/debug/libglean_ffi.dylib: ../src/lib.rs
+glean_app_release: $(SRC) $(OBJECTS_RELEASE) $(HEADERS)
+	$(CC) $(CFLAGS) -o $@ $(SRC) $(OBJECTS_RELEASE)
+
+$(OBJECTS_DEBUG): ../src/lib.rs
 	cargo build
 
-../../../target/release/libglean_ffi.dylib: ../src/lib.rs
+$(OBJECTS_RELEASE): ../src/lib.rs
 	cargo build --release

glean-core/ffi/examples/glean_app.c

@@ -3,12 +3,6 @@
 #include <stdlib.h>
 #include <string.h>
 
-// Not exported in glean.h right now.
-typedef struct ExternError {
-    uint32_t code;
-    char *message;
-} ExternError;
-
 #include "glean.h"
 
 int main(void)