scripts: adjust test-symbol-check for guix release environment

Now that our release binaries are build in a glibc 2.24 and 2.27
environment, we can't use a symbol from glibc 2.28 to test our checks.
Replace renameat2() with nextup(), which was introduced in 2.24.

Note that this also means re-disabling the test for RISC-V, however
RISC-V is built in a glibc 2.27 environment, and our minimum required
glibc for that binary is 2.27.

contrib/devtools/test-symbol-check.py

@@ -19,32 +19,39 @@ def call_symbol_check(cc: List[str], source, executable, options):
     os.remove(executable)
     return (p.returncode, p.stdout.rstrip())
 
+def get_machine(cc: List[str]):
+    p = subprocess.run([*cc,'-dumpmachine'], stdout=subprocess.PIPE, universal_newlines=True)
+    return p.stdout.rstrip()
+
 class TestSymbolChecks(unittest.TestCase):
     def test_ELF(self):
         source = 'test1.c'
         executable = 'test1'
         cc = determine_wellknown_cmd('CC', 'gcc')
 
-        # renameat2 was introduced in GLIBC 2.28, so is newer than the upper limit
-        # of glibc for all platforms
+        # there's no way to do this test for RISC-V at the moment; we build for
+        # RISC-V in a glibc 2.27 envinonment and we allow all symbols from 2.27.
+        if 'riscv' in get_machine(cc):
+            self.skipTest("test not available for RISC-V")
+
+        # nextup was introduced in GLIBC 2.24, so is newer than our supported
+        # glibc (2.17), and available in our release build environment (2.24).
         with open(source, 'w', encoding="utf8") as f:
             f.write('''
                 #define _GNU_SOURCE
-                #include <stdio.h>
-                #include <linux/fs.h>
+                #include <math.h>
 
-                int renameat2(int olddirfd, const char *oldpath,
-                    int newdirfd, const char *newpath, unsigned int flags);
+                double nextup(double x);
 
                 int main()
                 {
-                    renameat2(0, "test", 0, "test_", RENAME_EXCHANGE);
+                    nextup(3.14);
                     return 0;
                 }
         ''')
 
-        self.assertEqual(call_symbol_check(cc, source, executable, []),
-                (1, executable + ': symbol renameat2 from unsupported version GLIBC_2.28\n' +
+        self.assertEqual(call_symbol_check(cc, source, executable, ['-lm']),
+                (1, executable + ': symbol nextup from unsupported version GLIBC_2.24\n' +
                     executable + ': failed IMPORTED_SYMBOLS'))
 
         # -lutil is part of the libc6 package so a safe bet that it's installed