COMP: Do not add -mcorei7 with Emscripten
COMP: Do not add -mcorei7 with Emscripten

To address:

  clang-6.0: warning: argument unused during compilation:
  '-march=corei7' [-Wunused-command-line-argument]

with Emscripten toolchain 1.39.4

hjmjohnson/ITK,hjmjohnson/ITK,malaterre/ITK,malaterre/ITK,thewtex/ITK,richardbeare/ITK,Kitware/ITK,thewtex/ITK,InsightSoftwareConsortium/ITK,LucasGandel/ITK,malaterre/ITK,malaterre/ITK,BRAINSia/ITK,vfonov/ITK,vfonov/ITK,LucasGandel/ITK,Kitware/ITK,BRAINSia/ITK,richardbeare/ITK,hjmjohnson/ITK,Kitware/ITK,BRAINSia/ITK,LucasGandel/ITK,InsightSoftwareConsortium/ITK,BRAINSia/ITK,malaterre/ITK,malaterre/ITK,richardbeare/ITK,Kitware/ITK,thewtex/ITK,hjmjohnson/ITK,LucasGandel/ITK,InsightSoftwareConsortium/ITK,richardbeare/ITK,hjmjohnson/ITK,malaterre/ITK,LucasGandel/ITK,thewtex/ITK,InsightSoftwareConsortium/ITK,InsightSoftwareConsortium/ITK,BRAINSia/ITK,Kitware/ITK,hjmjohnson/ITK,thewtex/ITK,thewtex/ITK,LucasGandel/ITK,InsightSoftwareConsortium/ITK,InsightSoftwareConsortium/ITK,vfonov/ITK,Kitware/ITK,vfonov/ITK,vfonov/ITK,vfonov/ITK,LucasGandel/ITK,thewtex/ITK,vfonov/ITK,hjmjohnson/ITK,Kitware/ITK,LucasGandel/ITK,vfonov/ITK,richardbeare/ITK,malaterre/ITK,vfonov/ITK,BRAINSia/ITK,richardbeare/ITK,malaterre/ITK,richardbeare/ITK,BRAINSia/ITK