Stub out a hand-assembled __unwind_info section.

The intention is to use this to simplify unit testing, rather than
relying on trying to derive specific output from the assembler itself,
which will often require exceeding certain limits (such as function or
encoding counts) to trigger behavior that is required for testing.

Resources/Tests/PLCrashAsyncCompactUnwindEncodingTests/test.c

@@ -0,0 +1,66 @@
+#include <mach-o/compact_unwind_encoding.h>
+#include <stddef.h>
+
+#define IMAGE_BASE 0x0
+
+struct unwind_sect_compressed_page {
+        struct unwind_info_compressed_second_level_page_header header;
+        uint32_t entries[1];
+};
+
+struct unwind_sect_regular_page {
+        struct unwind_info_regular_second_level_page_header header;
+        uint32_t entries[1];
+};
+
+struct unwind_sect {
+    struct unwind_info_section_header hdr;
+    struct unwind_info_section_header_index_entry entries[2];
+
+    struct unwind_sect_regular_page regular_page_1;
+
+    struct unwind_sect_compressed_page compressed_page_1;
+};
+
+struct unwind_sect data __attribute__((section("__TEXT,__unwind_info"))) = {
+    .hdr = {
+        .version = 1,
+        .commonEncodingsArraySectionOffset = 0,
+        .commonEncodingsArrayCount = 0,
+        .personalityArraySectionOffset = 0,
+        .personalityArrayCount = 0,
+        .indexSectionOffset = offsetof(struct unwind_sect, entries),
+        .indexCount = 2 // all tools treat this as indexCount - 1
+    },
+
+    .entries = { 
+        {
+            .functionOffset = 0,
+            .secondLevelPagesSectionOffset = offsetof(struct unwind_sect, compressed_page_1)
+        },
+        { } // empty/ignored entry
+    },
+
+    .regular_page_1 = {
+        .header = {
+            .kind = UNWIND_SECOND_LEVEL_REGULAR,
+            .entryPageOffset = offsetof(struct unwind_sect_regular_page, entries),
+            .entryCount = 1
+        },
+        .entries = {
+            0x0
+        }
+    },
+
+    .compressed_page_1 = {
+        .header = {
+            .kind = UNWIND_SECOND_LEVEL_COMPRESSED,
+            .entryPageOffset = offsetof(struct unwind_sect_compressed_page, entries),
+            .entryCount = 1
+        },
+        .entries = {
+            0x0
+        },
+    },
+};
+