[ORC] Add read operations to orc::MemoryAccess.

[lhames]

This commit adds operations to orc::MemoryAccess for reading basic types (uint8_t, uint16_t, uint32_t, uint64_t, pointers, buffers, and strings) from executor memory.

The InProcessMemoryAccess and EPCGenericMemoryAccess implementations are updated to support the new operations.

[llvm-ci]

LLVM Buildbot has detected a new failure on builder clang-armv8-quick running on linaro-clang-armv8-quick while building llvm at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/154/builds/17956

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

Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'LLVM-Unit :: ExecutionEngine/Orc/./OrcJITTests/69/180' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/ExecutionEngine/Orc/./OrcJITTests-LLVM-Unit-541294-69-180.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=180 GTEST_SHARD_INDEX=69 /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/ExecutionEngine/Orc/./OrcJITTests
--

Note: This is test shard 70 of 180.
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from EPCGenericMemoryAccessTest
[ RUN      ] EPCGenericMemoryAccessTest.WritePointers
 #0 0x09386d88 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/ExecutionEngine/Orc/./OrcJITTests+0xb36d88)
 #1 0x0938450c llvm::sys::RunSignalHandlers() (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/ExecutionEngine/Orc/./OrcJITTests+0xb3450c)
 #2 0x09387654 SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
 #3 0xeb9fd6f0 __default_rt_sa_restorer ./signal/../sysdeps/unix/sysv/linux/arm/sigrestorer.S:80:0
 #4 0x0967db80 testing::Test::Run() (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/ExecutionEngine/Orc/./OrcJITTests+0xe2db80)
 #5 0x0967f034 testing::TestInfo::Run() (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/ExecutionEngine/Orc/./OrcJITTests+0xe2f034)
 #6 0x0967fd54 testing::TestSuite::Run() (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/ExecutionEngine/Orc/./OrcJITTests+0xe2fd54)
 #7 0x09691c98 testing::internal::UnitTestImpl::RunAllTests() (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/ExecutionEngine/Orc/./OrcJITTests+0xe41c98)
 #8 0x09691218 testing::UnitTest::Run() (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/ExecutionEngine/Orc/./OrcJITTests+0xe41218)
 #9 0x0965e9b8 main (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/ExecutionEngine/Orc/./OrcJITTests+0xe0e9b8)
#10 0xeb9ed7d6 __libc_start_call_main ./csu/../sysdeps/nptl/libc_start_call_main.h:74:3
#11 0xeb9ed886 call_init ./csu/libc-start.c:128:20
#12 0xeb9ed886 __libc_start_main ./csu/libc-start.c:379:5

--
exit: -11
--
shard JSON output does not exist: /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/ExecutionEngine/Orc/./OrcJITTests-LLVM-Unit-541294-69-180.json
********************