Allow LLVM built without some of Zig's default targets. The missing ones get
no-op initialisers, so Zig reports them as unavailable instead of failing to
configure.

diff -ru a/CMakeLists.txt b/CMakeLists.txt
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -494,6 +494,13 @@
 target_compile_features(zigcpp PRIVATE cxx_std_17)
 set_target_properties(zigcpp PROPERTIES POSITION_INDEPENDENT_CODE ${ZIG_PIE})
 
+if(ZIG_LLVM_MISSING_TARGETS)
+  message(STATUS "LLVM lacks targets ${ZIG_LLVM_MISSING_TARGETS}, Zig cannot generate code for them")
+  list(TRANSFORM ZIG_LLVM_MISSING_TARGETS REPLACE "(.+)" "ZIG_LLVM_STUB_TARGET(\\1)" OUTPUT_VARIABLE _stubs)
+  list(JOIN _stubs " " _stubs)
+  target_compile_definitions(zigcpp PRIVATE "ZIG_LLVM_MISSING_TARGETS=${_stubs}")
+endif()
+
 if(LLVM_LINK_MODE STREQUAL "static")
   target_compile_definitions(zigcpp PRIVATE
     LLVM_BUILD_STATIC
diff -ru a/cmake/Findllvm.cmake b/cmake/Findllvm.cmake
--- a/cmake/Findllvm.cmake
+++ b/cmake/Findllvm.cmake
@@ -85,22 +85,14 @@
 
     set(ZIG_LLVM_REQUIRED_TARGETS "AArch64;AMDGPU;ARM;AVR;BPF;Hexagon;Lanai;LoongArch;Mips;MSP430;NVPTX;PowerPC;RISCV;SPIRV;Sparc;SystemZ;VE;WebAssembly;X86;XCore")
 
-    set(ZIG_LLVM_REQUIRED_TARGETS_ENABLED TRUE)
+    # Targets LLVM was built without get no-op initialisers in zigcpp
+    set(ZIG_LLVM_MISSING_TARGETS "")
     foreach(TARGET_NAME IN LISTS ZIG_LLVM_REQUIRED_TARGETS)
       list (FIND LLVM_TARGETS_BUILT "${TARGET_NAME}" _index)
       if (${_index} EQUAL -1)
-        # Save the error message, in case this is the last llvm-config we find
-        list(APPEND LLVM_CONFIG_ERROR_MESSAGES "LLVM (according to ${LLVM_CONFIG_EXE}) is missing target ${TARGET_NAME}. Zig requires LLVM to be built with all default targets enabled.")
-
-        # Ignore this directory and try the search again
-        list(APPEND CMAKE_IGNORE_PATH "${LLVM_CONFIG_DIR}")
-        set(ZIG_LLVM_REQUIRED_TARGETS_ENABLED FALSE)
-        break()
+        list(APPEND ZIG_LLVM_MISSING_TARGETS "${TARGET_NAME}")
       endif()
     endforeach()
-    if (NOT ZIG_LLVM_REQUIRED_TARGETS_ENABLED)
-      continue()
-    endif()
 
     # Got it!
     break()
diff -ru a/src/zig_llvm.cpp b/src/zig_llvm.cpp
--- a/src/zig_llvm.cpp
+++ b/src/zig_llvm.cpp
@@ -546,3 +546,13 @@
 static_assert((object::Archive::Kind)ZigLLVMArchiveKind_DARWIN64 == object::Archive::Kind::K_DARWIN64, "");
 static_assert((object::Archive::Kind)ZigLLVMArchiveKind_COFF == object::Archive::Kind::K_COFF, "");
 static_assert((object::Archive::Kind)ZigLLVMArchiveKind_AIXBIG == object::Archive::Kind::K_AIXBIG, "");
+
+#ifdef ZIG_LLVM_MISSING_TARGETS
+#define ZIG_LLVM_STUB_TARGET(T) \
+    extern "C" void LLVMInitialize##T##Target(void) {} \
+    extern "C" void LLVMInitialize##T##TargetInfo(void) {} \
+    extern "C" void LLVMInitialize##T##TargetMC(void) {} \
+    extern "C" void LLVMInitialize##T##AsmPrinter(void) {} \
+    extern "C" void LLVMInitialize##T##AsmParser(void) {}
+ZIG_LLVM_MISSING_TARGETS
+#endif