Fix typo in get_linux_sysroot that makes cross-compilation fail

Author: xtremekforever

utils/swift_build_support/swift_build_support/products/product.py

@@ -373,7 +373,7 @@ def get_linux_target_components(self, arch):
     def get_linux_sysroot(self, platform, arch):
         if not self.is_cross_compile_target('{}-{}'.format(platform, arch)):
             return None
-        sysroot_arch, abi = self.get_linux_target_components(arch)
+        sysroot_arch, _, abi = self.get_linux_target_components(arch)
         # $ARCH-$PLATFORM-$ABI
         # E.x.: aarch64-linux-gnu
         sysroot_dirname = '{}-{}-{}'.format(sysroot_arch, platform, abi)