Remove with-clang feature in favor of using $CC

Signed-off-by: Victor Porof <victor.porof@gmail.com>

.travis.yml

@@ -32,8 +32,7 @@ before_script:
 
 script:
   - cargo +nightly-2019-09-11 fmt --all -- --check
-  - cargo +nightly-2019-09-11 clippy --all-features -- -D warnings
-  - cargo build --features with-clang --verbose
+  - CC="clang" cargo +nightly-2019-09-11 clippy --all-features -- -D warnings
   - cargo build --verbose
   - export RUST_BACKTRACE=1
   - cargo test --all --verbose

Cargo.toml

@@ -16,7 +16,6 @@ exclude = ["/tests/envs/*"]
 [features]
 default = []
 backtrace = ["failure/backtrace", "failure/std"]
-with-clang = ["lmdb-rkv/with-clang"]
 with-asan = ["lmdb-rkv/with-asan"]
 with-fuzzer = ["lmdb-rkv/with-fuzzer"]
 with-fuzzer-no-link = ["lmdb-rkv/with-fuzzer-no-link"]