Write tests for new APE loader and fix bugs

- Add FreeBSD-specific mmap() flags
- Reduce size of the APE loader from 8kb to 4kb
- Work towards fixing the Makefile build on WSL
- Automate testing of APE no-modify-self behaviors
- Make the ape.S shell script code cleaner and tinier
- Improve the APE sanity check to test behavior better
- Fixed issue with ShowCrashReports() sigaltstack() on BSDs
- Delete symbols for S_MODE magnums which wasted compile time

If you checked out yesterday's APE commit, please run:

    rm -f /usr/bin/ape o/tmp/ape /tmp/ape "${TMPDIR:-/tmp}/ape"

Because this change fixes certain aspects of the new ABI. We don't have
automated migrations for APE loader versions yet. Thanks! You can also
download prebuilt binaries here:

- https://justine.lol/ape.elf    (Linux/FreeBSD/NetBSD/OpenBSD)
- https://justine.lol/ape.macho  (Apple)

Install the appropriate one as `/usr/bin/ape`.

ape/ape.lds

@@ -243,10 +243,12 @@ SECTIONS {
     /* Code that needs to be addressable in Real Mode */
     *(.text.real)
     KEEP(*(SORT_BY_NAME(.sort.text.real.*)))
+    /* Code we want earlier in the binary w/o modifications */
+    KEEP(*(.ape.loader))
     HIDDEN(_ereal = .);
-    . += 1;
-
 /*END: realmode addressability guarantee */
+/*BEGIN: morphable code */
+    . += 1;
 
     /* Normal Code */
     *(.start)
@@ -283,6 +285,7 @@ SECTIONS {
     /* Privileged code invulnerable to magic */
     KEEP(*(.ape.pad.privileged));
     . += . > 0 ? 1 : 0;
+/*END: morphable code */
     HIDDEN(__privileged_start = .);
     . += . > 0 ? 1 : 0;
     *(.privileged)
@@ -390,21 +393,6 @@ SECTIONS {
   } :Ram
 
 /*END:   file content that's loaded by o/s */
-/*BEGIN: payload (for now, only the APE loader) */
-  .payload ALIGN(64) : {
-    /* Loader */
-    HIDDEN(ape_loader = .);
-    KEEP(*(.ape.loader))
-    . = ALIGN(64);
-    HIDDEN(ape_loader_end = .);
-#if SupportsXnu()
-    HIDDEN(ape_loader_macho = .);
-    KEEP(*(.ape.loader-macho))
-    . = ALIGN(64);
-    HIDDEN(ape_loader_macho_end = .);
-#endif
-  }
-/*END: payload */
 /*BEGIN: bss memory void */
 
   .zip . : {
@@ -552,13 +540,14 @@ HIDDEN(ape_bss_filesz = 0);
 HIDDEN(ape_bss_memsz = SIZEOF(.bss));
 HIDDEN(ape_bss_align = PAGESIZE);
 
-SHSTUB2(ape_loader_dd_skip, RVA(ape_loader) / 64);
-SHSTUB2(ape_loader_dd_count, (ape_loader_end - ape_loader) / 64);
-
-#if SupportsXnu()
-SHSTUB2(ape_loader_macho_dd_skip, RVA(ape_loader_macho) / 64);
-SHSTUB2(ape_loader_macho_dd_count, (ape_loader_macho_end - ape_loader_macho) / 64);
-#endif
+/* we roundup here because xnu wants the file load segments page-aligned */
+/* but we don't want to add the nop padding to the ape program, so we'll */
+/* let ape.S dd read past the end of the file into the wrapping binaries */
+SHSTUB2(ape_loader_dd_skip, DEFINED(ape_loader) ? RVA(ape_loader) / 64 : 0);
+SHSTUB2(ape_loader_dd_count,
+        DEFINED(ape_loader_end)
+            ? ROUNDUP(ape_loader_end - ape_loader, PAGESIZE) / 64
+            : 0);
 
 #if SupportsXnu()
 SHSTUB2(ape_macho_dd_skip, RVA(ape_macho) / 8);