Make old C++ demangler asynchronous signal safe

It's now possible to safely print C++ backtraces from signal handlers.
This symbol demangler doesn't need malloc, tls, or even static memory.
Additionally, this change makes it 2x faster and adds test cases. It's
almost as performant and accurate as the libcxxabi implementation now.

libc/cosmo.h

@@ -6,6 +6,8 @@ errno_t cosmo_once(_Atomic(uint32_t) *, void (*)(void));
 int systemvpe(const char *, char *const[], char *const[]) libcesque;
 char *GetProgramExecutableName(void);
 void unleaf(void);
+int __demangle(char *, const char *, size_t);
+int __is_mangled(const char *);
 
 COSMOPOLITAN_C_END_
 #endif /* COSMOPOLITAN_LIBC_COSMO_H_ */

libc/runtime/isheap.c

@@ -29,7 +29,7 @@
  * @assume stack memory isn't stored beneath %rsp (-mno-red-zone)
  * @deprecated
  */
-optimizesize bool32 _isheap(void *p) {
+optimizesize bool32 _isheap(const void *p) {
   intptr_t x, y;
   x = kAutomapStart;
   y = x + kAutomapSize;

libc/runtime/runtime.h

@@ -110,9 +110,9 @@ void *_mapanon(size_t) attributeallocsize((1)) mallocesque;
 void *_mapshared(size_t) attributeallocsize((1)) mallocesque;
 void CheckForMemoryLeaks(void);
 void CheckForFileLeaks(void);
+bool32 _isheap(const void *);
 void __enable_threads(void);
 void __oom_hook(size_t);
-bool32 _isheap(void *);
 /* code morphing */
 void __morph_begin(void);
 void __morph_end(void);

test/libc/str/BUILD.mk

@@ -6,6 +6,7 @@ PKGS += TEST_LIBC_STR
 TEST_LIBC_STR_FILES := $(wildcard test/libc/str/*)
 TEST_LIBC_STR_SRCS_C = $(filter %.c,$(TEST_LIBC_STR_FILES))
 TEST_LIBC_STR_SRCS_CC = $(filter %.cc,$(TEST_LIBC_STR_FILES))
+TEST_LIBC_STR_INCS = $(filter %.inc,$(TEST_LIBC_STR_FILES))
 TEST_LIBC_STR_SRCS = $(TEST_LIBC_STR_SRCS_C) $(TEST_LIBC_STR_SRCS_CC)
 TEST_LIBC_STR_SRCS_TEST_C = $(filter %_test.c,$(TEST_LIBC_STR_FILES))
 TEST_LIBC_STR_SRCS_TEST_CC = $(filter %_test.cc,$(TEST_LIBC_STR_FILES))

test/libc/str/demangle_test.c

@@ -0,0 +1,58 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8                               :vi │
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2024 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "demangle_cases.inc"
+#include "libc/cosmo.h"
+#include "libc/macros.internal.h"
+#include "libc/stdio/internal.h"
+#include "libc/str/str.h"
+
+char got[65536];
+
+static void regenerate_cases(void) {
+  FILE *f = fopen("demangle_cases.inc", "w");
+  fprintf(f, "const char* demangle_cases[][2] = {\n");
+  for (int i = 0; i < ARRAYLEN(demangle_cases); ++i) {
+    const char *input = demangle_cases[i][0];
+    const char *want = demangle_cases[i][1];
+    if (__demangle(got, input, sizeof(got)) == -1) {
+      fprintf(f, "\n    // {%`'s,\n    //  %`'s},\n    // got error\n\n", input,
+              want);
+    } else if (!strcmp(want, got)) {
+      fprintf(f, "    {%`'s, %`'s},\n", input, got);
+    } else {
+      fprintf(f,
+              "\n    // {%`'s,\n    //  %`'s},\n    //  %`'s was returned\n\n",
+              input, want, got);
+    }
+    fflush(f);
+  }
+  fprintf(f, "};\n");
+  fclose(f);
+}
+
+int main() {
+  for (int i = 0; i < ARRAYLEN(demangle_cases); ++i) {
+    const char *input = demangle_cases[i][0];
+    const char *want = demangle_cases[i][1];
+    if (__demangle(got, input, sizeof(got)) == -1)
+      return 1;
+    if (strcmp(want, got))
+      return 2;
+  }
+}

test/posix/BUILD.mk

@@ -33,6 +33,7 @@ TEST_POSIX_DIRECTDEPS =				\
 	LIBC_PROC				\
 	LIBC_RUNTIME				\
 	LIBC_STDIO				\
+	LIBC_STR				\
 	LIBC_SYSV				\
 	LIBC_THREAD