[LLVM] Add support for building experimental targets (#43822)

Author: vchuravy

deps/llvm.mk

@@ -61,6 +61,7 @@ LLVM_LIB_FILE := libLLVMCodeGen.a
 
 # Figure out which targets to build
 LLVM_TARGETS := host;NVPTX;AMDGPU;WebAssembly;BPF
+LLVM_EXPERIMENTAL_TARGETS :=
 
 LLVM_CFLAGS :=
 LLVM_CXXFLAGS :=
@@ -83,6 +84,7 @@ LLVM_CXXFLAGS += $(CXXFLAGS)
 LLVM_CPPFLAGS += $(CPPFLAGS)
 LLVM_LDFLAGS += $(LDFLAGS)
 LLVM_CMAKE += -DLLVM_TARGETS_TO_BUILD:STRING="$(LLVM_TARGETS)" -DCMAKE_BUILD_TYPE="$(LLVM_CMAKE_BUILDTYPE)"
+LLVM_CMAKE += -DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD:STRING="$(LLVM_EXPERIMENTAL_TARGETS)"
 LLVM_CMAKE += -DLLVM_ENABLE_LIBXML2=OFF -DLLVM_HOST_TRIPLE="$(or $(XC_HOST),$(BUILD_MACHINE))"
 LLVM_CMAKE += -DLLVM_ENABLE_ZLIB=ON -DZLIB_LIBRARY="$(build_prefix)/lib"
 LLVM_CMAKE += -DCOMPILER_RT_ENABLE_IOS=OFF -DCOMPILER_RT_ENABLE_WATCHOS=OFF -DCOMPILER_RT_ENABLE_TVOS=OFF