[TableGen] Fix build failure by using int type for NextChar

[jurahul]

• Fixes an issue in [NFC][TableGen] Refactor preprocessor directive handling #102967,
  which inddvertently changed the type of NextChar from int to char, causing ppc64le build failures.

[jurahul]

Can one of you please review and merge the MR? It seems I inadvertently change the variable type to char, causing ppc64le build failures:

FAILED: lib/TableGen/CMakeFiles/LLVMTableGen.dir/TGLexer.cpp.o
ccache /home/buildbots/llvm-external-buildbots/workers/ppc64le-lld-multistage-test/ppc64le-lld-multistage-test/install/stage1/bin/clang++ -DGTEST_HAS_RTTI=0 -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-lld-multistage-test/ppc64le-lld-multistage-test/build/stage2/lib/TableGen -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-lld-multistage-test/ppc64le-lld-multistage-test/llvm-project/llvm/lib/TableGen -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-lld-multistage-test/ppc64le-lld-multistage-test/build/stage2/include -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-lld-multistage-test/ppc64le-lld-multistage-test/llvm-project/llvm/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-f ield-initializers -pedantic -Wno-long-long -Wc++98-compat-extra-semi -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG -std=c++17 -fno-exceptions -funwind-tables -fno-rtti -UNDEBUG -MD -MT lib/TableGen/CMakeFiles/LLVMTableGen.dir/TGLexer.cpp.o -MF lib/TableGen/CMakeFiles/LLVMTableGen.dir/TGLexer.cpp.o.d -o lib/TableGen/CMakeFiles/LLVMTableGen.dir/TGLexer.cpp.o -c /home/buildbots/llvm-external-buildbots/workers/ppc64le-lld-multistage-test/ppc64le-lld-multistage-test/llvm-project/llvm/lib/TableGen/TGLexer.cpp
/home/buildbots/llvm-external-buildbots/workers/ppc64le-lld-multistage-test/ppc64le-lld-multistage-test/llvm-project/llvm/lib/TableGen/TGLexer.cpp:654:57: error: result of comparison of constant -1 with expression of type 'char' is always false [-Werror,-Wtautological-constant-out-of-range-compare]
654 | if (NextChar == ' ' || NextChar == '\t' || NextChar == EOF ||
| ~~~~~~~~ ^ ~~~

[jurahul]

Its flagging comparison with EOF, I think EOF is -1 and char us likely unsigned on this platform.

[jurahul]

Awesome, thanks so much!