Make it possible to build bionic with -I instead of -isystem.

Various things:

* work around -Wnullability-completeness.
* use C++ casts in C++ and C casts in C.
* stop using attributes clang doesn't support (such as `warning`).
* remove duplicate definitions of XATTR_CREATE and XATTR_REPLACE.

Change-Id: I07649e46275b28a23ca477deea119fe843999533
diff --git a/libc/include/sys/mman.h b/libc/include/sys/mman.h
index 7a8aa89..934963f 100644
--- a/libc/include/sys/mman.h
+++ b/libc/include/sys/mman.h
@@ -38,7 +38,7 @@
 #define MAP_ANON  MAP_ANONYMOUS
 #endif
 
-#define MAP_FAILED ((void *)-1)
+#define MAP_FAILED __BIONIC_CAST(reinterpret_cast, void*, -1)
 
 #define MREMAP_MAYMOVE  1
 #define MREMAP_FIXED    2
@@ -50,26 +50,26 @@
 #define POSIX_MADV_DONTNEED   MADV_DONTNEED
 
 #if defined(__USE_FILE_OFFSET64)
-extern void* mmap(void*, size_t, int, int, int, off_t) __RENAME(mmap64) __INTRODUCED_IN(21);
+void* mmap(void*, size_t, int, int, int, off_t) __RENAME(mmap64) __INTRODUCED_IN(21);
 #else
-extern void* mmap(void*, size_t, int, int, int, off_t);
+void* mmap(void*, size_t, int, int, int, off_t);
 #endif
-extern void* mmap64(void*, size_t, int, int, int, off64_t) __INTRODUCED_IN(21);
+void* mmap64(void*, size_t, int, int, int, off64_t) __INTRODUCED_IN(21);
 
-extern int munmap(void*, size_t);
-extern int msync(const void*, size_t, int);
-extern int mprotect(const void*, size_t, int);
-extern void* mremap(void*, size_t, size_t, int, ...);
+int munmap(void*, size_t);
+int msync(const void*, size_t, int);
+int mprotect(const void*, size_t, int);
+void* mremap(void*, size_t, size_t, int, ...);
 
-extern int mlockall(int) __INTRODUCED_IN(17);
-extern int munlockall(void) __INTRODUCED_IN(17);
-extern int mlock(const void*, size_t);
-extern int munlock(const void*, size_t);
+int mlockall(int) __INTRODUCED_IN(17);
+int munlockall(void) __INTRODUCED_IN(17);
+int mlock(const void*, size_t);
+int munlock(const void*, size_t);
 
-extern int mincore(void*, size_t, unsigned char*);
+int mincore(void*, size_t, unsigned char*);
 
-extern int madvise(void*, size_t, int);
-extern int posix_madvise(void*, size_t, int) __INTRODUCED_IN(23);
+int madvise(void*, size_t, int);
+int posix_madvise(void*, size_t, int) __INTRODUCED_IN(23);
 
 __END_DECLS