title: How to remove Ninja's limit on parallel link jobs?
body: <p>I was using Ninja 1.8.2 on Debian 9 to build llvm-6.0 using llvm-5.0. </p>
  
  <p>When I inspected the CPU usage of my system, I found the CPU is not 100% used, and there's plenty memory left.</p>
  
  <p>After checking the output of cmake, I found it limiting the parallel linking jobs to 2 because the llvm running on my machine runs in parallel too.</p>
  
  <p>I want to try whether lifting that limit will enable my build to be faster, but there's hardly any document about that.</p>
  
  <p>Edit:</p>
  
  <p>I checked the content of the rules.ninja file in my build dir, and found these:</p>
  
  <pre><code>#############################################
  # Pools defined by global property JOB_POOLS
  
  pool link_job_pool
    depth = 2
  </code></pre>
  
  <p>I also checked the content of build.ninja and found this:</p>
  
  <pre><code>build lib/libLLVMDemangle.a: CXX_STATIC_LIBRARY_LINKER__LLVMDemangle lib/Demangle/CMakeFiles/LLVMDemangle.dir/ItaniumDemangle.cpp.o
    LANGUAGE_COMPILE_FLAGS = -Ofast -fPIC -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -std=c++1y -Wal       l -W -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wcovered-switch-default -W       non-virtual-dtor -Wdelete-non-virtual-dtor -Wstring-conversion -fcolor-diagnostics -ffunction-sections -fdata-sections -flto=thin -O3 -D       NDEBUG
    OBJECT_DIR = lib/Demangle/CMakeFiles/LLVMDemangle.dir
    POST_BUILD = :
    PRE_LINK = :
    TARGET_FILE = lib/libLLVMDemangle.a
    TARGET_PDB = LLVMDemangle.a.dbg
    pool = link_job_pool
  </code></pre>
  
  <p>It seems that other commands for linking all have the arg <code>pool</code>.</p>