[Support] Fix LEB128 test when building with MSVC (llvm#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
```

Author: aganea

llvm/unittests/Support/LEB128Test.cpp

@@ -147,20 +147,22 @@ TEST(LEB128Test, DecodeULEB128) {
 TEST(LEB128Test, DecodeInvalidULEB128) {
 #define EXPECT_INVALID_ULEB128(VALUE, ERROR_OFFSET)                            \
   do {                                                                         \
-    const uint8_t *Value = reinterpret_cast<const uint8_t *>(VALUE);           \
+    const char *DefaultValue = VALUE;                                          \
+    const uint8_t *Value = reinterpret_cast<const uint8_t *>(DefaultValue);    \
     const char *Error = nullptr;                                               \
     unsigned ErrorOffset = 0;                                                  \
     uint64_t Actual =                                                          \
         decodeULEB128(Value, &ErrorOffset, Value + strlen(VALUE), &Error);     \
     EXPECT_NE(Error, nullptr);                                                 \
     EXPECT_EQ(0ul, Actual);                                                    \
     EXPECT_EQ(ERROR_OFFSET, ErrorOffset);                                      \
-    Value = reinterpret_cast<const uint8_t *>(VALUE);                          \
+    Value = reinterpret_cast<const uint8_t *>(DefaultValue);                   \
     Error = nullptr;                                                           \
     Actual = decodeULEB128AndInc(Value, Value + strlen(VALUE), &Error);        \
     EXPECT_NE(Error, nullptr);                                                 \
     EXPECT_EQ(0ul, Actual);                                                    \
-    EXPECT_EQ(ERROR_OFFSET, Value - reinterpret_cast<const uint8_t *>(VALUE)); \
+    EXPECT_EQ(ERROR_OFFSET,                                                    \
+              Value - reinterpret_cast<const uint8_t *>(DefaultValue));        \
   } while (0)
 
   // Buffer overflow.
@@ -222,20 +224,22 @@ TEST(LEB128Test, DecodeSLEB128) {
 TEST(LEB128Test, DecodeInvalidSLEB128) {
 #define EXPECT_INVALID_SLEB128(VALUE, ERROR_OFFSET)                            \
   do {                                                                         \
-    const uint8_t *Value = reinterpret_cast<const uint8_t *>(VALUE);           \
+    const char *DefaultValue = VALUE;                                          \
+    const uint8_t *Value = reinterpret_cast<const uint8_t *>(DefaultValue);    \
     const char *Error = nullptr;                                               \
     unsigned ErrorOffset = 0;                                                  \
     uint64_t Actual =                                                          \
         decodeSLEB128(Value, &ErrorOffset, Value + strlen(VALUE), &Error);     \
     EXPECT_NE(Error, nullptr);                                                 \
     EXPECT_EQ(0ul, Actual);                                                    \
     EXPECT_EQ(ERROR_OFFSET, ErrorOffset);                                      \
-    Value = reinterpret_cast<const uint8_t *>(VALUE);                          \
+    Value = reinterpret_cast<const uint8_t *>(DefaultValue);                   \
     Error = nullptr;                                                           \
     Actual = decodeSLEB128AndInc(Value, Value + strlen(VALUE), &Error);        \
     EXPECT_NE(Error, nullptr);                                                 \
     EXPECT_EQ(0ul, Actual);                                                    \
-    EXPECT_EQ(ERROR_OFFSET, Value - reinterpret_cast<const uint8_t *>(VALUE)); \
+    EXPECT_EQ(ERROR_OFFSET,                                                    \
+              Value - reinterpret_cast<const uint8_t *>(DefaultValue));        \
   } while (0)
 
   // Buffer overflow.
@@ -257,7 +261,9 @@ TEST(LEB128Test, DecodeInvalidSLEB128) {
 TEST(LEB128Test, DecodeAndInc) {
 #define EXPECT_LEB128(FUN, VALUE, SIZE)                                        \
   do {                                                                         \
-    const uint8_t *V = reinterpret_cast<const uint8_t *>(VALUE), *P = V;       \
+    const char *DefaultValue = VALUE;                                          \
+    const uint8_t *V = reinterpret_cast<const uint8_t *>(DefaultValue),        \
+                  *P = V;                                                      \
     auto Expected = FUN(P), Actual = FUN##AndInc(P, P + strlen(VALUE));        \
     EXPECT_EQ(Actual, Expected);                                               \
     EXPECT_EQ(P - V, SIZE);                                                    \