Fix LLVM build with host gcc 13

Building LLVM with a host gcc 13 fails and suggests including <cstdint>
in external/apache2/llvm/dist/llvm/include/llvm/Support/Signals.h .
Instead of this, joerg@ su

Fix LLVM build with host gcc 13

Building LLVM with a host gcc 13 fails and suggests including <cstdint>
in external/apache2/llvm/dist/llvm/include/llvm/Support/Signals.h .
Instead of this, joerg@ suggested not modifying the llvm vendor branch
but instead working around this in our LLVM build infrastructure.

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Add LLVM and clang build system. It is enabled by MKLLVM=yes.
Upstream sources can be fetched by running "make checkout" in
src/external/bsd/llvm, they will be properly imported once the
integration

Add LLVM and clang build system. It is enabled by MKLLVM=yes.
Upstream sources can be fetched by running "make checkout" in
src/external/bsd/llvm, they will be properly imported once the
integration and missing features are sorted out.

show more ...