Build kdump only for 64-bit

It doesn't support 32-bit target. Build crashdump, kexec, and the kernel
only for 64-bit and disable the 32-bit variant.

Bug: N/A
Test: build for aosp_x86 and full
Change-Id: I3fafff4a1a45ab808aa3b8cd720925c6b8f4fef3

microdroid/Android.bp

@@ -90,9 +90,6 @@ android_system_image {
         "microdroid_property_contexts",
         "microdroid_service_contexts",
 
-        "microdroid_kexec",
-        "microdroid_crashdump_kernel",
-
         // TODO(b/195425111) these should be added automatically
         "libcrypto", // used by many (init_second_stage, microdroid_manager, toybox, etc)
         "liblzma", // used by init_second_stage
@@ -113,6 +110,8 @@ android_system_image {
                 "apkdmverity",
                 "authfs",
                 "authfs_service",
+                "microdroid_crashdump_kernel",
+                "microdroid_kexec",
                 "microdroid_manager",
                 "zipfuse",
             ],

microdroid/kdump/Android.bp

@@ -7,6 +7,7 @@ cc_binary {
     stem: "kexec",
     srcs: ["kexec.c"],
     installable: false,
+    compile_multilib: "64",
 }
 
 cc_binary {
@@ -15,11 +16,16 @@ cc_binary {
     srcs: ["crashdump.c"],
     static_executable: true,
     installable: false,
+    compile_multilib: "64",
 }
 
 android_filesystem {
     name: "microdroid_crashdump_initrd",
-    deps: ["microdroid_crashdump"],
+    multilib: {
+        lib64: {
+            deps: ["microdroid_crashdump"],
+        },
+    },
     dirs: [
         "dev",
         "proc",

microdroid/kdump/crashdump.c

@@ -80,7 +80,7 @@ int main() {
     if (fstat(vmcore, &statbuf) == -1) {
         FAIL("Failed to stat %s", DUMP_SOURCE);
     }
-    printf("Size is %ld bytes\n", (long)statbuf.st_size);
+    printf("Size is %ld bytes\n", statbuf.st_size);
 
     // sendfile(2) is faster, can't be used because /proc/vmcore doesn't support splice_read
     size_t dumped = 0;

microdroid/kdump/kernel/Android.bp

@@ -12,7 +12,7 @@ license {
 
 prebuilt_etc {
     name: "microdroid_crashdump_kernel",
-    src: "empty", // for other 32-bit architectures like x86 and arm
+    compile_multilib: "64",
     arch: {
         arm64: {
             src: "arm64/kernel-5.15",