__progname should be const char*, not char*.

Change-Id: I8e846872c30a712fbc05c8da59ffa1cec1be31a4
diff --git a/libc/bionic/libc_init_common.cpp b/libc/bionic/libc_init_common.cpp
index 6b4ae2c..71acc45 100644
--- a/libc/bionic/libc_init_common.cpp
+++ b/libc/bionic/libc_init_common.cpp
@@ -46,7 +46,7 @@
 extern "C" int __system_properties_init(void);
 
 // Not public, but well-known in the BSDs.
-char* __progname;
+const char* __progname;
 
 // Declared in <unistd.h>
 char** environ;
@@ -88,7 +88,7 @@
   environ = args.envp;
   errno = 0;
   __libc_auxv = args.auxv;
-  __progname = args.argv[0] ? args.argv[0] : const_cast<char*>("<unknown>");
+  __progname = args.argv[0] ? args.argv[0] : "<unknown>";
 
   // Get the main thread from TLS and add it to the thread list.
   pthread_internal_t* main_thread = __get_thread();