Cannot crosscompile for armv7#184

Cannot crosscompile ncurses-rs, because it compiles test program for armv7 and tries to execute it on x86_64. How to disable that? ``` [vlisivka@vlisivka ncurses-rs]$ TARGET_CC=/opt/scel/17.2/sysroots/x86_64-scelsdk-linux/usr/bin/arm-scel-linux-gnueabi/arm-scel-linux-gnueabi-gcc TARGET_CFLAGS='--sysroot=/opt/scel/17.2/sysroots/armv7ahf-neon-scel-linux-gnueabi -mcpu=cortex-a9 -mfpu=neon -mfloat-abi=hard -marm' RUST_BACKTRACE=1 cargo build --example ex_1 --target armv7-unknown-linux-gnueabihf Compiling ncurses v5.99.0 (/home/vlisivka/tmp/rust-ui/ncurses-rs) error: failed to run custom build command for `ncurses v5.99.0 (/home/vlisivka/tmp/rust-ui/ncurses-rs)` process didn't exit successfully: `/home/vlisivka/tmp/rust-ui/ncurses-rs/target/debug/build/ncurses-b8678d1a3a7c29b3/build-script-build` (exit code: 101) --- stdout cargo:rerun-if-env-changed=PKG_CONFIG_PATH cargo:rustc-link-lib=ncurses OPT_LEVEL = Some("0") TARGET = Some("armv7-unknown-linux-gnueabihf") HOST = Some("x86_64-unknown-linux-gnu") CC_armv7-unknown-linux-gnueabihf = None CC_armv7_unknown_linux_gnueabihf = None TARGET_CC = Some("/opt/scel/17.2/sysroots/x86_64-scelsdk-linux/usr/bin/arm-scel-linux-gnueabi/arm-scel-linux-gnueabi-gcc") CFLAGS_armv7-unknown-linux-gnueabihf = None CFLAGS_armv7_unknown_linux_gnueabihf = None TARGET_CFLAGS = Some("--sysroot=/opt/scel/17.2/sysroots/armv7ahf-neon-scel-linux-gnueabi -mcpu=cortex-a9 -mfpu=neon -mfloat-abi=hard -marm") CRATE_CC_NO_DEFAULTS = None DEBUG = Some("true") CARGO_CFG_TARGET_FEATURE = None --- stderr thread 'main' panicked at '/home/vlisivka/tmp/rust-ui/ncurses-rs/target/armv7-unknown-linux-gnueabihf/debug/build/ncurses-3eeeed0374790b74/out/chtype_size failed: Os { code: 8, kind: Other, message: "Exec format error" }', src/libcore/result.rs:997:5 stack backtrace: 0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39 1: std::sys_common::backtrace::_print at src/libstd/sys_common/backtrace.rs:70 2: std::panicking::default_hook::{{closure}} at src/libstd/sys_common/backtrace.rs:58 at src/libstd/panicking.rs:200 3: std::panicking::default_hook at src/libstd/panicking.rs:215 4: std::panicking::rust_panic_with_hook at src/libstd/panicking.rs:478 5: std::panicking::continue_panic_fmt at src/libstd/panicking.rs:385 6: rust_begin_unwind at src/libstd/panicking.rs:312 7: core::panicking::panic_fmt at src/libcore/panicking.rs:85 8: core::result::unwrap_failed at /rustc/fc50f328b0353b285421b8ff5d4100966387a997/src/libcore/macros.rs:17 9: <core::result::Result<T, E>>::expect at /rustc/fc50f328b0353b285421b8ff5d4100966387a997/src/libcore/result.rs:825 10: build_script_build::check_chtype_size at ./build.rs:106 11: build_script_build::main at ./build.rs:59 12: std::rt::lang_start::{{closure}} at /rustc/fc50f328b0353b285421b8ff5d4100966387a997/src/libstd/rt.rs:64 13: std::panicking::try::do_call at src/libstd/rt.rs:49 at src/libstd/panicking.rs:297 14: __rust_maybe_catch_panic at src/libpanic_unwind/lib.rs:87 15: std::rt::lang_start_internal at src/libstd/panicking.rs:276 at src/libstd/panic.rs:388 at src/libstd/rt.rs:48 16: std::rt::lang_start at /rustc/fc50f328b0353b285421b8ff5d4100966387a997/src/libstd/rt.rs:64 17: main 18: __libc_start_main at ../csu/libc-start.c:308 19: _start ```