[llvm] minor revisions to export annotation macro docs

[andrurogerz]

Purpose

Make some minor tweaks and clarifications to the LLVM_ABI export annotation docs.

Overview

1. Minor cleanup on wording throughout
2. Clarification around class-level annotation requirements to export vtable

Validation

Manually inspected docs on my fork here.

[andrurogerz]

@compnerd do you mind having a look at this doc revision? thanks!

[llvm-ci]

LLVM Buildbot has detected a new failure on builder llvm-clang-x86_64-gcc-ubuntu running on sie-linux-worker3 while building llvm at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/174/builds/17460

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

Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'AddressSanitizer-x86_64-linux-dynamic :: TestCases/asan_lsan_deadlock.cpp' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
/home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/./bin/clang  --driver-mode=g++ -fsanitize=address -mno-omit-leaf-frame-pointer -fno-omit-frame-pointer -fno-optimize-sibling-calls -gline-tables-only  -m64  -shared-libasan -O0 /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/compiler-rt/test/asan/TestCases/asan_lsan_deadlock.cpp -o /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/runtimes/runtimes-bins/compiler-rt/test/asan/X86_64LinuxDynamicConfig/TestCases/Output/asan_lsan_deadlock.cpp.tmp # RUN: at line 4
+ /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/./bin/clang --driver-mode=g++ -fsanitize=address -mno-omit-leaf-frame-pointer -fno-omit-frame-pointer -fno-optimize-sibling-calls -gline-tables-only -m64 -shared-libasan -O0 /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/compiler-rt/test/asan/TestCases/asan_lsan_deadlock.cpp -o /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/runtimes/runtimes-bins/compiler-rt/test/asan/X86_64LinuxDynamicConfig/TestCases/Output/asan_lsan_deadlock.cpp.tmp
env ASAN_OPTIONS=detect_leaks=1 not  /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/runtimes/runtimes-bins/compiler-rt/test/asan/X86_64LinuxDynamicConfig/TestCases/Output/asan_lsan_deadlock.cpp.tmp 2>&1 | FileCheck /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/compiler-rt/test/asan/TestCases/asan_lsan_deadlock.cpp # RUN: at line 5
+ FileCheck /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/compiler-rt/test/asan/TestCases/asan_lsan_deadlock.cpp
+ env ASAN_OPTIONS=detect_leaks=1 not /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/runtimes/runtimes-bins/compiler-rt/test/asan/X86_64LinuxDynamicConfig/TestCases/Output/asan_lsan_deadlock.cpp.tmp
�[1m/home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/compiler-rt/test/asan/TestCases/asan_lsan_deadlock.cpp:58:12: �[0m�[0;1;31merror: �[0m�[1mCHECK: expected string not found in input
�[0m // CHECK: SUMMARY: AddressSanitizer: stack-buffer-overflow
�[0;1;32m           ^
�[0m�[1m<stdin>:1:1: �[0m�[0;1;30mnote: �[0m�[1mscanning from here
�[0m=================================================================
�[0;1;32m^
�[0m�[1m<stdin>:2:10: �[0m�[0;1;30mnote: �[0m�[1mpossible intended match here
�[0m==3631469==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7bc854dde034 at pc 0x564ad6cc7220 bp 0x7bc852ffdce0 sp 0x7bc852ffdcd8
�[0;1;32m         ^
�[0m
Input file: <stdin>
Check file: /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/compiler-rt/test/asan/TestCases/asan_lsan_deadlock.cpp

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

Input was:
<<<<<<
�[1m�[0m�[0;1;30m            1: �[0m�[1m�[0;1;46m================================================================= �[0m
�[0;1;31mcheck:58'0     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
�[0m�[0;1;30m            2: �[0m�[1m�[0;1;46m==3631469==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7bc854dde034 at pc 0x564ad6cc7220 bp 0x7bc852ffdce0 sp 0x7bc852ffdcd8 �[0m
�[0;1;31mcheck:58'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
�[0m�[0;1;35mcheck:58'1              ?                                                                                                                                    possible intended match
�[0m�[0;1;30m            3: �[0m�[1m�[0;1;46mWRITE of size 4 at 0x7bc854dde034 thread T2 �[0m
�[0;1;31mcheck:58'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
�[0m>>>>>>

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