This adds the providesSymbol method to DynamicLibrary. It returns
whether the library contains a function with the given name.
As per dlsym(3), it is valid for dlsym to return nullptr in a success
case if the symbol actually has a NULL value. So I've changed the logic
to check for dlerror() after we invoke dlsym(), both in the existing
lookup and in the new method.
Closes https://github.com/dart-lang/sdk/issues/46192
TEST=tests/ffi(_2)/has_symbol_test.dart
Change-Id: Ibcb1c051cc0cdd95a104fe86ef2fc76da5bafb5d
Cq-Include-Trybots: luci.dart.try:vm-precomp-ffi-qemu-linux-release-arm-try,vm-ffi-android-debug-arm64-try,vm-ffi-android-debug-arm-try,vm-kernel-linux-debug-x64-try,vm-kernel-win-debug-x64-try,vm-kernel-mac-debug-x64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/201900
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Commit-Queue: Daco Harkes <dacoharkes@google.com>
