Merge bitcoin/bitcoin#22238: build: improve detection of eBPF support

8f7704d032 build: improve detection of eBPF support (fanquake)

Pull request description:

  Just checking for the `sys/sdt.h` header isn't enough, as systems like macOS have the header, but it doesn't actually have the `DTRACE_PROBE*` probes, which leads to [compile failures](https://github.com/bitcoin/bitcoin/pull/22006#issuecomment-859559004). The contents of `sys/sdt.h` in the macOS SDK is:
  ```bash
  #ifndef _SYS_SDT_H
  #define _SYS_SDT_H

  /*
   * This is a wrapper header that wraps the mach visible sdt.h header so that
   * the header file ends up visible where software expects it to be.  We also
   * do the C/C++ symbol wrapping here, since Mach headers are technically C
   * interfaces.
   *
   * Note:  The process of adding USDT probes to code is slightly different
   * than documented in the "Solaris Dynamic Tracing Guide".
   * The DTRACE_PROBE*() macros are not supported on Mac OS X -- instead see
   * "BUILDING CODE CONTAINING USDT PROBES" in the dtrace(1) manpage
   *
   */
  #include <sys/cdefs.h>
  __BEGIN_DECLS
  #include <mach/sdt.h>
  __END_DECLS

  #endif  /* _SYS_SDT_H */
  ```

  The `BUILDING CODE CONTAINING USDT PROBES` section from the dtrace manpage is available [here](https://gist.github.com/fanquake/e56c9866d53b326646d04ab43a8df9e2), and outlines the more involved process of using USDT probes on macOS.

ACKs for top commit:
  jb55:
    utACK 8f7704d032
  practicalswift:
    cr ACK 8f7704d032
  hebasto:
    ACK 8f7704d032, tested on macOS Big Sur 11.4 (20F71) and on Linux Mint 20.1 (x86_64) with depends.

Tree-SHA512: 5f1351d0ac2e655fccb22a5454f415906404fdaa336fd89b54ef49ca50a442c44ab92d063cba3f161cb8ea0679c92ae3cd6cfbbcb19728cac21116247a017df5

configure.ac

@@ -1359,13 +1359,15 @@ if test x$enable_wallet != xno; then
 fi
 
 if test x$use_ebpf != xno; then
-  AC_CHECK_HEADER([sys/sdt.h], [have_sdt=yes], [have_sdt=no])
-else
-  have_sdt=no
-fi
-
-if test x$have_sdt = xyes; then
-  AC_DEFINE([ENABLE_TRACING], [1], [Define to 1 to enable eBPF user static defined tracepoints])
+  AC_MSG_CHECKING([whether eBPF tracepoints are supported])
+  AC_COMPILE_IFELSE([
+    AC_LANG_PROGRAM(
+      [#include <sys/sdt.h>],
+      [DTRACE_PROBE("context", "event");]
+    )],
+    [AC_MSG_RESULT(yes); have_sdt=yes; AC_DEFINE([ENABLE_TRACING], [1], [Define to 1 to enable eBPF user static defined tracepoints])],
+    [AC_MSG_RESULT(no); have_sdt=no;]
+  )
 fi
 
 dnl Check for libminiupnpc (optional)