Add <stdbool.h> to llvm-libc-types headers that need it. (llvm#165798)

We need `<stdbool.h>` to support having "bool" members inside pthread
structs that may get included through `<pthread.h>` from C code prior to
C23.

Author: vonosmas

libc/include/llvm-libc-types/__barrier_type.h

@@ -9,6 +9,8 @@
 #ifndef LLVM_LIBC_TYPES__BARRIER_TYPE_H
 #define LLVM_LIBC_TYPES__BARRIER_TYPE_H
 
+#include <stdbool.h>
+
 typedef struct __attribute__((aligned(8 /* alignof (Barrier) */))) {
   unsigned expected;
   unsigned waiting;

libc/include/llvm-libc-types/pthread_barrierattr_t.h

@@ -9,6 +9,8 @@
 #ifndef LLVM_LIBC_TYPES_PTHREAD_BARRIERATTR_T_H
 #define LLVM_LIBC_TYPES_PTHREAD_BARRIERATTR_T_H
 
+#include <stdbool.h>
+
 typedef struct {
   bool pshared;
 } pthread_barrierattr_t;