[runtimes] Allow passing individual parameters to the default target runtimes/builtins

[mstorsjo]

Summary

Currently, one can pass extra parameters to builds of runtimes
for specific targets, by setting them as e.g.
RUNTIMES_<targetname>_CMAKE_CXX_FLAGS. When not setting
LLVM_RUNTIME_TARGETS (or when it is set to "default"), no flags
are propagated in this way, but one can pass a set of cmake flags
to set via RUNTIMES_CMAKE_ARGS though.

While RUNTIMES_CMAKE_ARGS gives almost the same abilities, it's
slightly more cumbersome less obvious. (This flag is only available
for the runtimes, but not for the builtins.)

Thus, in addition to that existing flag, allow using the same pattern
of prefixing variables with "RUNTIMES_<targetname>_" and
"BUILTINS_<targetname>_", with targetname set to "default".

[mstorsjo]

Ping @phosek

[phosek]

LGTM after I land D117263 (I still need to figure out why it's failing on Windows), this would let us merge builtin_default_target with builtin_register_target and runtime_default_target with runtime_register_target thus removing a lot of the existing duplication.

llvm/runtimes/CMakeLists.txt

macro(set_enable_per_target_runtime_dir)
   endif()
 endmacro()
 
 function(builtin_default_target compiler_rt_path)
   cmake_parse_arguments(ARG "" "" "DEPENDS" ${ARGN})
 
   set_enable_per_target_runtime_dir()
 
+  get_cmake_property(variableNames VARIABLES)
+  foreach(variableName ${variableNames})
+    string(FIND "${variableName}" "BUILTINS_default" out)
+    if("${out}" EQUAL 0)
+      string(REPLACE "BUILTINS_default_" "" new_name ${variableName})
+      string(REPLACE ";" "|" new_value "${${variableName}}")
+      list(APPEND default_target_extra_args "-D${new_name}=${new_value}")
+    endif()
+  endforeach()
+
   llvm_ExternalProject_Add(builtins
                            ${compiler_rt_path}/lib/builtins
                            DEPENDS ${ARG_DEPENDS}
                            CMAKE_ARGS -DLLVM_LIBRARY_OUTPUT_INTDIR=${LLVM_LIBRARY_DIR}
                                       -DLLVM_RUNTIME_OUTPUT_INTDIR=${LLVM_TOOLS_BINARY_DIR}
                                       -DLLVM_DEFAULT_TARGET_TRIPLE=${LLVM_TARGET_TRIPLE}
                                       -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=${LLVM_ENABLE_PER_TARGET_RUNTIME_DIR}
                                       -DCMAKE_C_COMPILER_WORKS=ON
                                       -DCMAKE_ASM_COMPILER_WORKS=ON
                                       ${COMMON_CMAKE_ARGS}
                                       ${BUILTINS_CMAKE_ARGS}
+                                      ${default_target_extra_args}
                            PASSTHROUGH_PREFIXES COMPILER_RT
                                                 DARWIN
                                                 SANITIZER
                            USE_TOOLCHAIN
                            TARGET_TRIPLE ${LLVM_TARGET_TRIPLE}
                            ${EXTRA_ARGS})
 endfunction()
 
foreach(runtime_name ${runtime_names})
     endif()
   endforeach()
   foreach(component ${LLVM_RUNTIME_DISTRIBUTION_COMPONENTS})
     if(NOT ${component} IN_LIST SUB_COMPONENTS)
       list(APPEND extra_targets install-${component} install-${component}-stripped)
     endif()
   endforeach()
 
+  set(default_target_extra_args ${ARG_CMAKE_ARGS})
+  get_cmake_property(variableNames VARIABLES)
+  foreach(variableName ${variableNames})
+    string(FIND "${variableName}" "RUNTIMES_default_" out)
+    if("${out}" EQUAL 0)
+      string(REPLACE "RUNTIMES_default_" "" new_name ${variableName})
+      string(REPLACE ";" "|" new_value "${${variableName}}")
+      list(APPEND default_target_extra_args "-D${new_name}=${new_value}")
+    endif()
+  endforeach()
+
   if(LLVM_INCLUDE_TESTS)
     set_property(GLOBAL APPEND PROPERTY LLVM_ALL_LIT_TESTSUITES "@${LLVM_BINARY_DIR}/runtimes/runtimes-bins/lit.tests")
     list(APPEND test_targets runtimes-test-depends check-runtimes)
   endif()
 
   set_enable_per_target_runtime_dir()
 
   llvm_ExternalProject_Add(runtimes
                            ${CMAKE_CURRENT_SOURCE_DIR}/../../runtimes
                            DEPENDS ${ARG_DEPENDS}
                            # Builtins were built separately above
                            CMAKE_ARGS -DCOMPILER_RT_BUILD_BUILTINS=Off
                                       -DLLVM_INCLUDE_TESTS=${LLVM_INCLUDE_TESTS}
                                       -DLLVM_DEFAULT_TARGET_TRIPLE=${LLVM_TARGET_TRIPLE}
                                       -DLLVM_ENABLE_PROJECTS_USED=${LLVM_ENABLE_PROJECTS_USED}
                                       -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=${LLVM_ENABLE_PER_TARGET_RUNTIME_DIR}
                                       -DLLVM_BUILD_TOOLS=${LLVM_BUILD_TOOLS}
                                       -DCMAKE_C_COMPILER_WORKS=ON
                                       -DCMAKE_CXX_COMPILER_WORKS=ON
                                       -DCMAKE_ASM_COMPILER_WORKS=ON
                                       ${COMMON_CMAKE_ARGS}
                                       ${RUNTIMES_CMAKE_ARGS}
-                                      ${ARG_CMAKE_ARGS}
+                                      ${default_target_extra_args}
                            PASSTHROUGH_PREFIXES LLVM_ENABLE_RUNTIMES
                                                 LLVM_USE_LINKER
                                                 ${ARG_PREFIXES}
                            EXTRA_TARGETS ${extra_targets}
                                          ${test_targets}
                                          ${SUB_COMPONENTS}
                                          ${SUB_CHECK_TARGETS}
                                          ${SUB_INSTALL_TARGETS}