Fix internal uses of _PATH_BSHELL.

We regressed on this recently: code under the upstream-* directories has
_PATH_BSHELL defined as a call to __bionic_get_shell_path(). In our own
code, we may as well just call it directly.

Bug: https://issuetracker.google.com/129030706
Test: ran tests
Change-Id: Ic2423f521272be95e67f94771772fe8072636ef0
diff --git a/libc/stdio/stdio.cpp b/libc/stdio/stdio.cpp
index d7b69dc..d482a91 100644
--- a/libc/stdio/stdio.cpp
+++ b/libc/stdio/stdio.cpp
@@ -52,6 +52,7 @@
 
 #include "local.h"
 #include "glue.h"
+#include "private/__bionic_get_shell_path.h"
 #include "private/bionic_fortify.h"
 #include "private/ErrnoRestorer.h"
 #include "private/thread_private.h"
@@ -1226,7 +1227,7 @@
     if (dup2(fds[child], desired_child_fd) == -1) _exit(127);
     close(fds[child]);
     if (bidirectional) dup2(STDOUT_FILENO, STDIN_FILENO);
-    execl(_PATH_BSHELL, "sh", "-c", cmd, nullptr);
+    execl(__bionic_get_shell_path(), "sh", "-c", cmd, nullptr);
     _exit(127);
   }