[Support] Fix LEB128 test when building with MSVC (#93184)

The VALUE expansion might be compiled in the different ways, because of
string pooling which isn't always enabled/guaranteed. When building with
MSVC, previously I was seeing for example empty strings `""` pointing to
different addresses, thus the negative offsets below in the log.

Previous test log:
```
Note: Google Test filter = LEB128Test.DecodeInvalidULEB128
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from LEB128Test
[ RUN      ] LEB128Test.DecodeInvalidULEB128
C:\src\git\llvm-project\llvm\unittests\Support\LEB128Test.cpp(167): error: Expected equality of these values:
  0u
    Which is: 0
  Value - reinterpret_cast<const uint8_t *>("")
    Which is: -5

C:\src\git\llvm-project\llvm\unittests\Support\LEB128Test.cpp(168): error: Expected equality of these values:
  1u
    Which is: 1
  Value - reinterpret_cast<const uint8_t *>("\x80")
    Which is: -167

C:\src\git\llvm-project\llvm\unittests\Support\LEB128Test.cpp(171): error: Expected equality of these values:
  9u
    Which is: 9
  Value - reinterpret_cast<const uint8_t *>("\x80\x80\x80\x80\x80\x80\x80\x80\x80\x02")
    Which is: -167

C:\src\git\llvm-project\llvm\unittests\Support\LEB128Test.cpp(172): error: Expected equality of these values:
  10u
    Which is: 10
  Value - reinterpret_cast<const uint8_t *>("\x80\x80\x80\x80\x80\x80\x80\x80\x80\x80\x02")
    Which is: -166

[  FAILED  ] LEB128Test.DecodeInvalidULEB128 (2 ms)
[----------] 1 test from LEB128Test (2 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test suite ran. (4 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] LEB128Test.DecodeInvalidULEB128

 1 FAILED TEST
```