meson: only run symbols-check if nm is available

And drop the redundant check from symbols-check.py, which was actually
masking all kinds of issues.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35891>
(cherry picked from commit 4be493862d)

.pick_status.json

@@ -7944,7 +7944,7 @@
         "description": "meson: only run symbols-check if `nm` is available",
         "nominated": false,
         "nomination_type": 0,
-        "resolution": 4,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": null,
         "notes": null

bin/symbols-check.py

@@ -140,7 +140,6 @@ def main():
                         help='do not process this symbol')
     args = parser.parse_args()
 
-    try:
     if platform.system() == 'Windows':
         if not args.dumpbin:
             parser.error('--dumpbin is mandatory')
@@ -149,10 +148,7 @@ def main():
         if not args.nm:
             parser.error('--nm is mandatory')
         lib_symbols = get_symbols_nm(args.nm, args.lib)
-    except:
+
-        # We can't run this test, but we haven't technically failed it either
-        # Return the GNU "skip" error code
-        exit(77)
     mandatory_symbols = []
     optional_symbols = []
     with open(args.symbols_file) as symbols_file:

meson.build

@@ -2277,7 +2277,7 @@ if host_machine.system() == 'windows'
   endif
 else
   prog_nm = find_program('nm')
-  with_symbols_check = with_tests
+  with_symbols_check = prog_nm.found() and with_tests
   symbols_check_args = ['--nm', prog_nm.full_path()]
 endif