[readtapi][tests] add descriptions to tests (llvm#73576)

(cherry picked from commit 4d29bda)

Author: cyndyishida

llvm/test/tools/llvm-readtapi/command-line.test

@@ -1,6 +1,8 @@
 ; RUN: llvm-readtapi --help 2>&1 | FileCheck %s 
 ; RUN: llvm-readtapi -help 2>&1 | FileCheck %s 
+// Check mutually exclusive options.
 ; RUN: not llvm-readtapi -merge -compare -compact %t/tmp.tbd %t/tmp2.tbd 2>&1 | FileCheck %s --check-prefix MULTI_ACTION
+// Check unsupported file output format.
 ; RUN: not llvm-readtapi -merge -compact %t/tmp.tbd %t/tmp2.tbd --filetype=tbd-v2 2>&1 | FileCheck %s --check-prefix FILE_FORMAT 
 
 CHECK: OVERVIEW: LLVM TAPI file reader and manipulator

llvm/test/tools/llvm-readtapi/extract-invalid.test

@@ -1,7 +1,10 @@
 ; RUN: rm -rf %t
 ; RUN: split-file %s %t
+// Check readtapi only accepts one file. 
 ; RUN: not llvm-readtapi -extract %t/libfoo.tbd %t/libbar.tbd 2>&1 | FileCheck %s --allow-empty --check-prefix EXTRA
+// Check missing argument.
 ; RUN: not llvm-readtapi -extract %t/libfoo.tbd 2>&1 | FileCheck %s --allow-empty --check-prefix MISSING
+// Check that TBD file manipulation was not valid and error propagated as expected.
 ; RUN: not llvm-readtapi -arch x86_64 -extract %t/libfoo.tbd 2>&1 | FileCheck %s --allow-empty --check-prefix MISMATCH 
 
 ; EXTRA: error: extract only supports one input file

llvm/test/tools/llvm-readtapi/merge-invalid.test

@@ -1,6 +1,8 @@
 ; RUN: rm -rf %t
 ; RUN: split-file %s %t
+// Check invalid tbd file contents was propagated as error.
 ; RUN: not llvm-readtapi -merge %t/libfoo.tbd %t/libbar.tbd 2>&1 | FileCheck %s --allow-empty --check-prefix DIFF
+// Check missing input.
 ; RUN: not llvm-readtapi -merge %t/libfoo.tbd 2>&1 | FileCheck %s --allow-empty --check-prefix INPUT
 
 ; DIFF: install names do not match

llvm/test/tools/llvm-readtapi/remove.test

@@ -1,5 +1,7 @@
 ; RUN: rm -rf %t
 ; RUN: split-file %s %t 
+// Check that arch removal is accepted with tbdv5 and various inlined contents.
+
 ; RUN: llvm-readtapi --remove -arch x86_64h %t/libfat.tbd -o %t/libslim.tbd 2>&1 | FileCheck --allow-empty %s
 ; RUN: llvm-readtapi --compare %t/libslim.tbd %t/libslim_expected.tbd