Bring back gc() function

Renaming gc() to _gc() was a mistake since the better thing to do is put
it behind the _COSMO_SOURCE macro. We need this change because I haven't
wanted to use my amazing garbage collector ever since we renamed it. You
now need to define _COSMO_SOURCE yourself when using amalgamation header
and cosmocc users need to pass the -mcosmo flag to get the gc() function

Some other issues relating to cancelation have been fixed along the way.
We're also now putting cosmocc in a folder named `.cosmocc` so it can be
more safely excluded by grep --exclude-dir=.cosmocc --exclude-dir=o etc.

test/libc/thread/makecontext_test.c

@@ -20,7 +20,7 @@
 #include "libc/calls/ucontext.h"
 #include "libc/dce.h"
 #include "libc/limits.h"
-#include "libc/mem/gc.internal.h"
+#include "libc/mem/gc.h"
 #include "libc/nt/createfile.h"
 #include "libc/nt/enum/accessmask.h"
 #include "libc/nt/enum/creationdisposition.h"

test/libc/thread/pthread_atfork_test.c

@@ -19,7 +19,7 @@
 #include "libc/calls/calls.h"
 #include "libc/dce.h"
 #include "libc/mem/gc.h"
-#include "libc/mem/gc.internal.h"
+#include "libc/mem/gc.h"
 #include "libc/mem/mem.h"
 #include "libc/runtime/internal.h"
 #include "libc/runtime/runtime.h"

test/libc/thread/pthread_barrier_wait_test.c

@@ -20,7 +20,7 @@
 #include "libc/atomic.h"
 #include "libc/errno.h"
 #include "libc/intrin/atomic.h"
-#include "libc/mem/gc.internal.h"
+#include "libc/mem/gc.h"
 #include "libc/mem/mem.h"
 #include "libc/runtime/runtime.h"
 #include "libc/testlib/testlib.h"

test/libc/thread/pthread_cancel_test.c

@@ -232,7 +232,7 @@ void *CpuBoundWorker(void *arg) {
   wontleak1 = malloc(123);
   (void)wontleak1;
   pthread_cleanup_push(free, wontleak1);
-  wontleak2 = _gc(malloc(123));
+  wontleak2 = gc(malloc(123));
   (void)wontleak2;
   ASSERT_EQ(0, pthread_setspecific(key, (void *)31337));
   ASSERT_EQ(0, pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, 0));

test/libc/thread/pthread_create_test.c

@@ -29,7 +29,7 @@
 #include "libc/limits.h"
 #include "libc/macros.internal.h"
 #include "libc/mem/gc.h"
-#include "libc/mem/gc.internal.h"
+#include "libc/mem/gc.h"
 #include "libc/mem/mem.h"
 #include "libc/nexgen32e/nexgen32e.h"
 #include "libc/nexgen32e/vendor.internal.h"
@@ -177,8 +177,8 @@ TEST(pthread_create, testCustomStack_withReallySmallSize) {
 void *JoinMainWorker(void *arg) {
   void *rc;
   pthread_t main_thread = (pthread_t)arg;
-  _gc(malloc(32));
-  _gc(malloc(32));
+  gc(malloc(32));
+  gc(malloc(32));
   ASSERT_EQ(0, pthread_join(main_thread, &rc));
   ASSERT_EQ(123, (intptr_t)rc);
   return 0;
@@ -186,8 +186,8 @@ void *JoinMainWorker(void *arg) {
 
 TEST(pthread_join, mainThread) {
   pthread_t id;
-  _gc(malloc(32));
-  _gc(malloc(32));
+  gc(malloc(32));
+  gc(malloc(32));
   SPAWN(fork);
   ASSERT_EQ(0, pthread_create(&id, 0, JoinMainWorker, (void *)pthread_self()));
   pthread_exit((void *)123);
@@ -196,8 +196,8 @@ TEST(pthread_join, mainThread) {
 
 TEST(pthread_join, mainThreadDelayed) {
   pthread_t id;
-  _gc(malloc(32));
-  _gc(malloc(32));
+  gc(malloc(32));
+  gc(malloc(32));
   SPAWN(fork);
   ASSERT_EQ(0, pthread_create(&id, 0, JoinMainWorker, (void *)pthread_self()));
   usleep(10000);

test/libc/thread/pthread_rwlock_rdlock_test.c

@@ -18,7 +18,7 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/atomic.h"
 #include "libc/mem/gc.h"
-#include "libc/mem/gc.internal.h"
+#include "libc/mem/gc.h"
 #include "libc/mem/mem.h"
 #include "libc/testlib/testlib.h"
 #include "libc/thread/thread.h"

test/libc/thread/sem_open_test.c

@@ -86,7 +86,7 @@ void *Worker(void *arg) {
 TEST(sem_open, test) {
   sem_t *a, *b;
   int i, r, n = 8;
-  pthread_t *t = _gc(malloc(sizeof(pthread_t) * n));
+  pthread_t *t = gc(malloc(sizeof(pthread_t) * n));
   errno = 0;
   ASSERT_EQ(0, pthread_barrier_init(&barrier, 0, n));
   ASSERT_NE(SEM_FAILED, (a = sem_open(name1, O_CREAT, 0644, 0)));

test/libc/thread/sem_timedwait_test.c

@@ -104,7 +104,7 @@ void *Worker(void *arg) {
 TEST(sem_timedwait, threads) {
   int i, r, n = 4;
   sem_t sm[2], *s[2] = {sm, sm + 1};
-  pthread_t *t = _gc(malloc(sizeof(pthread_t) * n));
+  pthread_t *t = gc(malloc(sizeof(pthread_t) * n));
   ASSERT_SYS(0, 0, sem_init(s[0], 0, 0));
   ASSERT_SYS(0, 0, sem_init(s[1], 0, 0));
   for (i = 0; i < n; ++i) ASSERT_EQ(0, pthread_create(t + i, 0, Worker, s));