New option --catch-sigsegv on amd64, arm64, arm.v4a

Catch SIGSEGV during de-compression, and print state info
("auto debug") using /proc/self/maps and gdb.
This was motivated by suspicion of unreliable hardware
which triggered "Heisenbugs": a crash which cannot be reproduced.
If SIGSGV occurs without the "auto debug" info, then that
implies an error user code after de-compression, often when
user code accesses /proc/self/exe, which is not the un-compressed file.
	modified:   misc/testsuite/upx_testsuite_1-expected_sha256sums.sh
	modified:   src/help.cpp
	modified:   src/main.cpp
	modified:   src/options.h
	modified:   src/p_lx_elf.cpp
	modified:   src/stub/Makefile
	modified:   src/stub/src/amd64-linux.elf-entry.S
	modified:   src/stub/src/amd64-linux.elf-fold.S
	modified:   src/stub/src/arm.v4a-linux.elf-entry.S
	modified:   src/stub/src/arm.v4a-linux.elf-fold.S
	modified:   src/stub/src/arm64-linux.elf-entry.S
	modified:   src/stub/src/arm64-linux.elf-fold.S
           plus generated .h .dump .map

src/help.cpp

@@ -342,6 +342,7 @@ void show_help(int verbose) {
         fg = con_fg(f, fg);
         con_fprintf(f,
                     "  --preserve-build-id     copy .gnu.note.build-id to compressed output\n"
+                    "  --catch-sigsegv         debug errors in hardware or de-compressor\n"
                     "\n");
     }
     // clang-format on