add macos catalyst support

[sercand]

Closes #471.

Due to #408 as described here, cc treats compiler as gnu compiler and still fails to add required flags. We still need manually set CXX as a workaround.

[alexcrichton]

Thanks!

[eranrund]

Hello @sercand and @alexcrichton !

Sorry to bring up this old PR, but I'm wondering about a decision made in it. Looking at https://github.com/alexcrichton/cc-rs/pull/556/files#diff-b1a35a68f14e696205874893c07fd24fdb88882b47c23cc0e0c80a30c7d53759R1466, I am curious why the arm64 version uses ios vs ios13.0 on x64.

I ran into this while trying to build mbedtls for the target aarch64-apple-ios-macabi. With ios, I am getting the following error:

[mbedtls-sys-auto 2.26.1] cd /Users/eran/Projects/fog/target/aarch64-apple-ios-macabi/release/build/mbedtls-sys-auto-32061b327ca02d13/out/build/library && /usr/bin/clang  -I/Users/eran/.cargo/git/checkouts/rust-mbedtls-83053073cf3ce6f5/1cc2220/mbedtls-sys/vendor/include -I/Users/eran/.cargo/git/checkouts/rust-mbedtls-83053073cf3ce6f5/1cc2220/mbedtls-sys/vendor/library -DMBEDTLS_CONFIG_FILE="\"/Users/eran/Projects/fog/target/aarch64-apple-ios-macabi/release/build/mbedtls-sys-auto-32061b327ca02d13/out/config.h\"" -fPIC --target=arm64-apple-ios-macabi -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.3.sdk -fembed-bitcode -Wall -Wextra -Wwrite-strings -Wpointer-arith -Wimplicit-fallthrough -Wshadow -Wvla -Wformat=2 -Wno-format-nonliteral -Werror -Wmissing-declarations -Wmissing-prototypes -Wdocumentation -Wno-documentation-deprecated-sync -Wunreachable-code -O2 -g -DNDEBUG -arch arm64 -MD -MT library/CMakeFiles/mbedcrypto.dir/threading.c.o -MF CMakeFiles/mbedcrypto.dir/threading.c.o.d -o CMakeFiles/mbedcrypto.dir/threading.c.o -c /Users/eran/.cargo/git/checkouts/rust-mbedtls-83053073cf3ce6f5/1cc2220/mbedtls-sys/vendor/library/threading.c
[mbedtls-sys-auto 2.26.1] /Users/eran/.cargo/git/checkouts/rust-mbedtls-83053073cf3ce6f5/1cc2220/mbedtls-sys/vendor/library/threading.c:76:23: error: 'pthread_mutex_init' is only available on macCatalyst 13.0 or newer [-Werror,-Wunguarded-availability-new]
[mbedtls-sys-auto 2.26.1]     mutex->is_valid = pthread_mutex_init( &mutex->mutex, NULL ) == 0;

As expected, moving to ios13.0 fixes it and I am able to build. Perhaps this should be configurable, if not simply bumped to 13.0?

Thanks!