base-linux: 64-bit ARM support

This patch adds support for running Genode/Linux on the AARCH64
architecture.

- The kernel-agnostic startup code (crt0) had to be extended to
  capture the initial stack pointer, which the Linux kernel uses
  to pass the process environment. This is in line with the
  existing startup code for x86_32 and x86_64.

- The link order of the host libraries linked to lx_hybrid
  programs had to be adjusted such that libgcc appears at last
  because the other libraries depend on symbols provided by
  libgcc.

- When using AARCH64 Linux as host, one can execute run scripts
  via 'make run/<script> KERNEL=linux BOARD=linux' now.

Issue #4136

repos/base-linux/src/core/include/core_linux_syscalls.h

@@ -60,6 +60,11 @@ inline int lx_open(char const *pathname, int flags, mode_t mode = 0)
 
 inline int lx_stat_size(char const *path, Genode::uint64_t &out_size)
 {
+#ifdef __aarch64__
+	struct statx buf { };
+	int result = lx_syscall(SYS_statx, AT_FDCWD, path, 0, STATX_SIZE, &buf);
+	out_size = buf.stx_size;
+#else
 #ifdef _LP64
 	struct stat buf { };
 	int result = lx_syscall(SYS_stat, path, &buf);
@@ -68,6 +73,7 @@ inline int lx_stat_size(char const *path, Genode::uint64_t &out_size)
 	struct stat64 buf { };
 	int result = lx_syscall(SYS_stat64, path, &buf);
 	out_size = buf.st_size;
+#endif
 #endif
 	return result;
 }