[llvm] Proofread YamlIO.rst

[kazutakahirata]

This patch only adds double backticks around code-related terms to
facilitate the review process.

[llvm-ci]

LLVM Buildbot has detected a new failure on builder llvm-clang-x86_64-expensive-checks-debian running on gribozavr4 while building llvm at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/16/builds/23215

Here is the relevant piece of the build log for the reference

Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: TableGen/RuntimeLibcallEmitter.td' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llvm-tblgen -gen-runtime-libcalls -I /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/TableGen/../../include /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/TableGen/RuntimeLibcallEmitter.td | /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/FileCheck /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/TableGen/RuntimeLibcallEmitter.td # RUN: at line 1
+ /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llvm-tblgen -gen-runtime-libcalls -I /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/TableGen/../../include /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/TableGen/RuntimeLibcallEmitter.td
+ /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/FileCheck /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/TableGen/RuntimeLibcallEmitter.td
/b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/TableGen/RuntimeLibcallEmitter.td:98:16: error: CHECK-NEXT: expected string not found in input
// CHECK-NEXT: sqrtl_f80 = 7, // sqrtl
               ^
<stdin>:32:23: note: scanning from here
 calloc = 6, // calloc
                      ^
<stdin>:34:2: note: possible intended match here
 sqrtl_f80 = 8, // sqrtl
 ^

Input file: <stdin>
Check file: /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/TableGen/RuntimeLibcallEmitter.td

-dump-input=help explains the following input dump.

Input was:
<<<<<<
           .
           .
           .
          27:  ___memcpy = 1, // ___memcpy 
          28:  ___memset = 2, // ___memset 
          29:  __ashlsi3 = 3, // __ashlsi3 
          30:  __lshrdi3 = 4, // __lshrdi3 
          31:  bzero = 5, // bzero 
          32:  calloc = 6, // calloc 
next:98'0                           X error: no match found
          33:  sqrtl_f128 = 7, // sqrtl 
next:98'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~
          34:  sqrtl_f80 = 8, // sqrtl 
next:98'0     ~~~~~~~~~~~~~~~~~~~~~~~~~
next:98'1      ?                        possible intended match
          35:  NumLibcallImpls = 9 
next:98'0     ~~~~~~~~~~~~~~~~~~~~~
          36: }; 
next:98'0     ~~~
          37: } // End namespace RTLIB 
next:98'0     ~~~~~~~~~~~~~~~~~~~~~~~~~
          38: } // End namespace llvm 
next:98'0     ~~~~~~~~~~~~~~~~~~~~~~~~
          39: #endif 
next:98'0     ~~~~~~~
...