Support for the mold linker (XRPLF#4807)

Builds/CMake/RippledCompiler.cmake

@@ -131,7 +131,16 @@ else ()
       >)
 endif ()
 
-if (use_gold AND is_gcc)
+if (use_mold)
+  # use mold linker if available
+  execute_process (
+    COMMAND ${CMAKE_CXX_COMPILER} -fuse-ld=mold -Wl,--version
+    ERROR_QUIET OUTPUT_VARIABLE LD_VERSION)
+  if ("${LD_VERSION}" MATCHES "mold")
+    target_link_libraries (common INTERFACE -fuse-ld=mold)
+  endif ()
+  unset (LD_VERSION)
+elseif (use_gold AND is_gcc)
   # use gold linker if available
   execute_process (
     COMMAND ${CMAKE_CXX_COMPILER} -fuse-ld=gold -Wl,--version
@@ -163,9 +172,7 @@ if (use_gold AND is_gcc)
         $<$<NOT:$<BOOL:${static}>>:-Wl,--disable-new-dtags>)
   endif ()
   unset (LD_VERSION)
-endif ()
-
-if (use_lld)
+elseif (use_lld)
   # use lld linker if available
   execute_process (
     COMMAND ${CMAKE_CXX_COMPILER} -fuse-ld=lld -Wl,--version
@@ -176,6 +183,7 @@ if (use_lld)
   unset (LD_VERSION)
 endif()
 
+
 if (assert)
   foreach (var_ CMAKE_C_FLAGS_RELEASE CMAKE_CXX_FLAGS_RELEASE)
     STRING (REGEX REPLACE "[-/]DNDEBUG" "" ${var_} "${${var_}}")

Builds/CMake/RippledSettings.cmake

@@ -37,6 +37,7 @@ if (is_linux)
   option (static "link protobuf, openssl, libc++, and boost statically" ON)
   option (perf "Enables flags that assist with perf recording" OFF)
   option (use_gold "enables detection of gold (binutils) linker" ON)
+  option (use_mold "enables detection of mold (binutils) linker" ON)
 else ()
   # we are not ready to allow shared-libs on windows because it would require
   # export declarations. On macos it's more feasible, but static openssl
@@ -45,6 +46,7 @@ else ()
   set (static ON CACHE BOOL "static link, linux only. ON for WIN/macos" FORCE)
   set (perf OFF CACHE BOOL "perf flags, linux only" FORCE)
   set (use_gold OFF CACHE BOOL "gold linker, linux only" FORCE)
+  set (use_mold OFF CACHE BOOL "mold linker, linux only" FORCE)
 endif ()
 if (is_clang)
   option (use_lld "enables detection of lld linker" ON)