build: add arg to disable linking against -latomic

building using `clang` with `compiler-rt` fails with an error due to `-latomic` being added even when it is not needed:
```
ld.lld: error: unable to find library -latomic
```

Ideally, the build would run a link test to determine if `-latomic` is needed and does not add `-latomic`,  when the compiler runtime provides atomic builtin. This workaround adds `--without_libatomic` to manually disable `-latomic`.

Bug: #65900
Signed-off-by: Pepper Gray <hello@peppergray.xyz>

Author: peppergrayxyz

BUILDING.md

@@ -380,6 +380,9 @@ may reduce build time. For more information, see the
 The above requires that `python` resolves to a supported version of
 Python. See [Prerequisites](#prerequisites).
 
+> Note: When the compiler runtime provides atomic builtins, such as with compiler-rt (llvm),
+> passing `--without-libatomic` disables linking against `libatomic` (`-latomic`).
+
 After building, setting up [firewall rules](tools/macos-firewall.sh) can avoid
 popups asking to accept incoming network connections when running tests.
 

common.gypi

@@ -22,6 +22,7 @@
     'force_dynamic_crt%': 0,
     'node_use_v8_platform%': 'true',
     'node_use_bundled_v8%': 'true',
+    'node_use_libatomic%': 'true',
     'node_module_version%': '',
     'node_with_ltcg%': '',
     'node_shared_openssl%': 'false',

configure.py

@@ -1120,6 +1120,13 @@
     default=None,
     help='build without FFI (Foreign Function Interface) support')
 
+parser.add_argument('--without-libatomic', '--without_libatomic',
+    action='store_true',
+    dest='without_libatomic',
+    default=None,
+    help='do not link against libatomic when the compiler runtime ' +
+         'provides atomic builtins (e.g. compiler-rt)')
+
 parser.add_argument('--experimental-quic',
     action='store_true',
     dest='experimental_quic',
@@ -1907,6 +1914,7 @@ def configure_node(o):
   o['variables']['node_install_corepack'] = b(options.with_corepack)
   o['variables']['control_flow_guard'] = b(options.enable_cfg)
   o['variables']['node_use_amaro'] = b(not options.without_amaro)
+  o['variables']['node_use_libatomic'] = b(not options.without_libatomic)
   o['variables']['debug_node'] = b(options.debug_node)
   o['variables']['debug_symbols'] = b(options.debug_symbols)
   if options.debug_symbols:

node.gyp

@@ -578,7 +578,7 @@
           '-Wl,-bnoerrmsg',
         ],
       }],
-      ['OS=="linux" and clang==1', {
+      ['OS=="linux" and clang==1 and node_use_libatomic=="true"', {
         'libraries': ['-latomic'],
       }],
     ],

tools/v8_gypfiles/v8.gyp

@@ -1404,7 +1404,7 @@
         # Platforms that don't have Compare-And-Swap (CAS) support need to link atomic library
         # to implement atomic memory access.
         # Clang needs it for some atomic operations (https://clang.llvm.org/docs/Toolchain.html#atomics-library).
-        ['(OS=="linux" and clang==1) or (v8_current_cpu in ["mips64", "mips64el", "arm", "riscv64", "loong64"])', {
+        ['((OS=="linux" and clang==1) or (v8_current_cpu in ["mips64", "mips64el", "arm", "riscv64", "loong64"])) and node_use_libatomic=="true"', {
           'link_settings': {
             'libraries': ['-latomic', ],
           },