build-llvm: Disable CLANG_ENABLE_CIR

In recent git versions of llvm-project, this option (enabling
the new experimental ClangIR feature) defaults to true.

Disable it in our builds; ClangIR is still experimental.

Building with ClangIR enabled currently breaks builds for a mingw
target, if dylibs is enabled. (Dylibs are enabled in all builds of
llvm-mingw currently. Dylibs makes the build significantly
smaller, ending up at a zip file size around 156 MB instead of
399 MB, for one sample.)

If building with ClangIR enabled, with dylibs, for a mingw target,
the build fails with "ld.lld: error: too many exported symbols
(got 94721, max 65535)", for libclang-cpp.dll. Without ClangIR
enabled, the number of exported symbols from libclang-cpp.dll
currently is around 43306.

build-llvm.sh

@@ -403,6 +403,7 @@ cmake \
     -DLLVM_TARGETS_TO_BUILD="ARM;AArch64;X86;NVPTX" \
     -DLLVM_INSTALL_TOOLCHAIN_ONLY=$TOOLCHAIN_ONLY \
     -DLLVM_LINK_LLVM_DYLIB=$LINK_DYLIB \
+    -DCLANG_ENABLE_CIR=OFF \
     -DLLVM_TOOLCHAIN_TOOLS="llvm-ar;llvm-ranlib;llvm-objdump;llvm-rc;llvm-cvtres;llvm-nm;llvm-strings;llvm-readobj;llvm-dlltool;llvm-pdbutil;llvm-objcopy;llvm-strip;llvm-cov;llvm-profdata;llvm-addr2line;llvm-symbolizer;llvm-windres;llvm-ml;llvm-readelf;llvm-size;llvm-cxxfilt;llvm-lib" \
     ${HOST+-DLLVM_HOST_TRIPLE=$HOST} \
     -DLLVM_BUILD_INSTRUMENTED=$INSTRUMENTED \