[core] Use __attribute__((noinline)) on IIFE lambdas to honor attribute

The C++ standard-attribute spelling [[gnu::noinline]] placed between a
lambda's parameter list and body binds to the return type, not the
call operator. GCC 14 silently ignores it and emits -Wattributes
warnings at every chunk site. Switch to GCC's __attribute__((...))
syntax which binds to operator() as intended.

Measured impact on apollo-r-pro-1-eth (esp32-s3, -Os) vs the broken
[[gnu::noinline]] version: setup() frame 160 B -> 32 B, peak stack
304 B -> 176 B (another -42%). Flash grows by 888 B because all 86
chunks now stay as separate functions instead of GCC inlining the
small ones (which it was free to do when the attribute was ignored).

Net vs baseline -Os: peak stack 1264 B -> 176 B (-86%); flash
+388 B (<0.05% of a typical esp32 partition).

esphome/core/__init__.py

@@ -532,12 +532,17 @@ class Library:
 
 
 def _wrap_in_noinline_iifes(lines: list[str], max_statements: int) -> list[str]:
-    """Wrap ``lines`` in one or more ``[]() [[gnu::noinline]] { ... }();`` IIFEs.
+    """Wrap ``lines`` in one or more ``[]() __attribute__((noinline)) {...}();`` IIFEs.
 
     Splits into IIFEs of up to ``max_statements`` entries each. Never splits
     inside a brace-balanced block (e.g. the ``{`` / ``}`` pair that
     ``cg.with_local_variable()`` emits around a scoped local), so an IIFE
     may exceed ``max_statements`` when a block straddles the boundary.
+
+    GCC note: ``__attribute__((noinline))`` between the lambda parameter
+    list and body binds to ``operator()``. The C++ standard-attribute
+    spelling ``[[gnu::noinline]]`` in that position binds to the return
+    type instead and produces ``-Wattributes`` warnings.
     """
     out: list[str] = []
     chunk: list[str] = []
@@ -546,7 +551,7 @@ def _wrap_in_noinline_iifes(lines: list[str], max_statements: int) -> list[str]:
     def flush() -> None:
         if not chunk:
             return
-        out.append("[]() [[gnu::noinline]] {")
+        out.append("[]() __attribute__((noinline)) {")
         out.extend(chunk)
         out.append("}();")
         chunk.clear()

tests/unit_tests/test_core.py

@@ -877,7 +877,7 @@ def test_wrap_in_noinline_iifes_empty_input() -> None:
 def test_wrap_in_noinline_iifes_fewer_lines_than_limit() -> None:
     lines = ["a();", "b();", "c();"]
     assert core._wrap_in_noinline_iifes(lines, max_statements=10) == [
-        "[]() [[gnu::noinline]] {",
+        "[]() __attribute__((noinline)) {",
         "a();",
         "b();",
         "c();",
@@ -896,13 +896,13 @@ def test_wrap_in_noinline_iifes_never_splits_inside_braces() -> None:
     # max=2 would naively split after "{" but brace guard keeps block whole.
     lines = ["a();", "{", "inner();", "}", "b();"]
     assert core._wrap_in_noinline_iifes(lines, max_statements=2) == [
-        "[]() [[gnu::noinline]] {",
+        "[]() __attribute__((noinline)) {",
         "a();",
         "{",
         "inner();",
         "}",
         "}();",
-        "[]() [[gnu::noinline]] {",
+        "[]() __attribute__((noinline)) {",
         "b();",
         "}();",
     ]
@@ -911,14 +911,14 @@ def test_wrap_in_noinline_iifes_never_splits_inside_braces() -> None:
 def test_wrap_in_noinline_iifes_nested_braces() -> None:
     lines = ["{", "{", "deep();", "}", "}", "after();"]
     assert core._wrap_in_noinline_iifes(lines, max_statements=1) == [
-        "[]() [[gnu::noinline]] {",
+        "[]() __attribute__((noinline)) {",
         "{",
         "{",
         "deep();",
         "}",
         "}",
         "}();",
-        "[]() [[gnu::noinline]] {",
+        "[]() __attribute__((noinline)) {",
         "after();",
         "}();",
     ]
@@ -929,7 +929,7 @@ def test_wrap_in_noinline_iifes_unbalanced_braces_fall_through() -> None:
     # a single IIFE with all lines rather than splitting mid-flight.
     lines = ["a();", "}", "b();"]
     result = core._wrap_in_noinline_iifes(lines, max_statements=1)
-    assert result[0] == "[]() [[gnu::noinline]] {"
+    assert result[0] == "[]() __attribute__((noinline)) {"
     assert result[-1] == "}();"
     assert [line for line in result if line in lines] == lines
 
@@ -952,7 +952,7 @@ def test_cpp_main_section_component_marker_wraps_in_iife() -> None:
         RawStatement("new_wifi();"),
     ]
     out = target.cpp_main_section
-    assert out.count("[]() [[gnu::noinline]] {") == 2
+    assert out.count("[]() __attribute__((noinline)) {") == 2
     assert out.count("}();") == 2
     assert "// === logger ===" in out
     assert "// === wifi ===" in out
@@ -966,4 +966,4 @@ def test_cpp_main_section_prefix_statements_stay_outside_iife() -> None:
         RawStatement("body();"),
     ]
     out = target.cpp_main_section
-    assert out.index("prefix();") < out.index("[]() [[gnu::noinline]] {")
+    assert out.index("prefix();") < out.index("[]() __attribute__((noinline)) {")