Improve signals and memory protection

- Document sigaction()
- Simplify New Technology fork() code
- Testing and many bug fixes for mprotect()
- Distribute Intel Xed ILD in the amalgamation
- Turn Xed enums into defines to avoid DWARF bloat
- Improve polyfilling of SA_SIGINFO on BSDs and fix bugs
- setpgid(getpid(), getpid()) on Windows will ignore CTRL-C
- Work around issues relating to NT mappings being executable
- Permit automatic executable stack override via `ape_stack_pf`

libc/intrin/describeflags.internal.h

@@ -10,6 +10,11 @@ struct thatispacked DescribeFlags {
 
 const char *DescribeFlags(char *, size_t, struct DescribeFlags *, size_t,
                           const char *, unsigned);
+
+const char *DescribeMapFlags(int);
+const char *DescribeProtFlags(int);
+const char *DescribeRemapFlags(int);
+
 const char *DescribeNtPageFlags(uint32_t);
 const char *DescribeNtFileMapFlags(uint32_t);
 const char *DescribeNtFileFlagsAndAttributes(uint32_t);