Some cleanups in block to IMP conversion.

On FreeBSD (and other platforms that choose to implement the , allocate the
memory via the anonymous shared memory mechanism, removing the need for the
temporary file.  On other POSIX platforms, correctly use mkstemp().

block_to_imp.c

@@ -9,6 +9,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <unistd.h>
+#include <sys/types.h>
 #include <sys/mman.h>
 #include "objc/runtime.h"
 #include "objc/blocks_runtime.h"
@@ -28,17 +29,10 @@ static void *executeBuffer;
 static void *writeBuffer;
 static ptrdiff_t offset;
 static mutex_t trampoline_lock;
+#ifndef SHM_ANON
 static char *tmpPattern;
-
-struct wx_buffer
+static void initTmpFile(void)
 {
-	void *w;
-	void *x;
-};
-
-PRIVATE void init_trampolines(void)
-{
-	INIT_LOCK(trampoline_lock);
 	char *tmp = getenv("TMPDIR");
 	if (NULL == tmp)
 	{
@@ -49,14 +43,40 @@ PRIVATE void init_trampolines(void)
 		abort();
 	}
 }
+static int getAnonMemFd(void)
+{
+	const char *pattern = strdup(tmpPattern);
+	int fd = mkstemp(pattern);
+	unlink(pattern);
+	free(pattern);
+	return fd;
+}
+#else
+static void initTmpFile(void) {}
+static int getAnonMemFd(void)
+{
+	return shm_open(SHM_ANON, O_CREAT | O_RDWR, 0);
+}
+#endif
+
+struct wx_buffer
+{
+	void *w;
+	void *x;
+};
+
+PRIVATE void init_trampolines(void)
+{
+	INIT_LOCK(trampoline_lock);
+	initTmpFile();
+}
 
 static struct wx_buffer alloc_buffer(size_t size)
 {
 	LOCK_FOR_SCOPE(&trampoline_lock);
 	if ((0 == offset) || (offset + size >= PAGE_SIZE))
 	{
-		int fd = mkstemp(tmpPattern);
-		unlink(tmpPattern);
+		int fd = getAnonMemFd();
 		ftruncate(fd, PAGE_SIZE);
 		void *w = mmap(NULL, PAGE_SIZE, PROT_WRITE, MAP_SHARED, fd, 0);
 		executeBuffer = mmap(NULL, PAGE_SIZE, PROT_READ|PROT_EXEC, MAP_SHARED, fd, 0);