Apple-darwin: set DEBUG_LTO_BUILD_DOESNT_WORK

Temporary workaround for the well known
"undefined references problem for debug-assertions+lto" (#79)

.travis.yml

@@ -11,7 +11,7 @@ matrix:
     - env: TARGET=arm-unknown-linux-gnueabihf
     - env: TARGET=armv7-unknown-linux-gnueabihf
     - env: TARGET=i586-unknown-linux-gnu
-    - env: TARGET=i686-apple-darwin
+    - env: TARGET=i686-apple-darwin DEBUG_LTO_BUILD_DOESNT_WORK=1
       os: osx
     - env: TARGET=i686-unknown-linux-gnu
     - env: TARGET=mips-unknown-linux-gnu
@@ -28,7 +28,7 @@ matrix:
     - env: TARGET=wasm32-unknown-unknown
       install: rustup target add $TARGET
       script: cargo build --target $TARGET
-    - env: TARGET=x86_64-apple-darwin
+    - env: TARGET=x86_64-apple-darwin DEBUG_LTO_BUILD_DOESNT_WORK=1
       os: osx
     - env: TARGET=x86_64-unknown-linux-gnu
   allow_failures: