[lld-macho][nfc] Re-enable previously disabled test.

[oontvoo]

Summary

This check was previous disabled (in D139572) because the test kept failing on ARM64. The output from reported failure message
gave the impression that the bundle was created as an x86-64 bundle but upon further inspection, I believe that's
a bug in llvm-otool where it prints both -h and -f for both input files on ARM64.

So the "fix" here is to rewrite the test to run the two otool commands separately but concatenate the
output into one file for checking.

Tested this on all 3 platforms: Linux-x86-64, Mac x86-64 and Mac ARM64.

lld/test/MachO/fat-arch.s

 # CHECK: error: unable to find matching architecture in [[FILE]]
 
 ## Validates that we read the cpu-subtype correctly from a fat exec.
 # RUN: %lld -o %t.x86_64.out %t.x86_64.o
 # RUN: %lld -arch arm64 -o %t.arm64.out %t.arm64.o
 # RUN: llvm-lipo %t.x86_64.out %t.arm64.out -create -o %t.fat.exec.out
 # RUN: %lld -arch x86_64 %t.x86_64.o -bundle_loader %t.fat.exec.out -bundle -o %t.fat.bundle
 
-## FIXME: Re-enable this test, which is failing on arm64, once we figured out why
-## %t.fat.bundle is produced as an arm64.
-# RUN llvm-otool -h %t.fat.bundle -f %t.fat.exec.out | FileCheck %s --check-prefix=CPU-SUB
+# RUN: llvm-otool -h %t.fat.bundle > %t.bundle_header.txt
+# RUN: llvm-otool -f %t.fat.exec.out >> %t.bundle_header.txt
+# RUN: cat %t.bundle_header.txt | FileCheck %s --check-prefix=CPU-SUB
+
+# CPU-SUB:            magic     cputype      cpusubtype   caps      filetype   ncmds sizeofcmds      flags
+# CPU-SUB-NEXT:  0xfeedfacf     16777223              3  0x{{.+}}    {{.+}}  {{.+}}    {{.+}}      {{.+}}
+  
 # CPU-SUB: Fat headers
 # CPU-SUB: nfat_arch 2
 # CPU-SUB: architecture 0
 # CPU-SUB-NEXT:    cputype 16777223
 # CPU-SUB-NEXT:    cpusubtype 3
 # CPU-SUB: architecture 1
 # CPU-SUB-NEXT:    cputype 16777228
 # CPU-SUB-NEXT:    cpusubtype 0
 
-# CPU-SUB:            magic     cputype      cpusubtype   caps      filetype   ncmds sizeofcmds      flags
-# CPU-SUB-NEXT:  0xfeedfacf     16777223              3  0x{{.+}}    {{.+}}  {{.+}}    {{.+}}      {{.+}}
-
 .text
 .global _main
 _main:
   ret