make command name needs to be adjustable

[clausecker]

The bdw dependency requires GNU make to be built, but currently the build scripts just hard code make:

# build BDW garbage collector
option(CPLR_ENABLE_BDWGC "Enable BDW garbage collector as malloc replacement" ON)
if(CPLR_ENABLE_BDWGC)
  set(BDWGC_CONFIG --prefix=/bdwgc --enable-static --disable-shared --enable-replace-malloc)
  set(BDWGC_SOURCE_DIR ${CMAKE_SOURCE_DIR}/deps/bdwgc)
  # build bdwgc and install to stage
  ExternalProject_Add(bdwgc
    PREFIX ${DEPBLD}
    SOURCE_DIR ${BDWGC_SOURCE_DIR}
    DOWNLOAD_COMMAND true
    PATCH_COMMAND autoreconf -vi ${BDWGC_SOURCE_DIR}
    CONFIGURE_COMMAND ${BDWGC_SOURCE_DIR}/configure ${BDWGC_CONFIG} && make clean
    BUILD_COMMAND make all
    INSTALL_COMMAND make install DESTDIR=${STAGE}
    )
  # determine includes and libs
  set(BDWGC_INCLUDE_DIRS ${STAGE}/bdwgc/include)
  set(BDWGC_LDFLAGS ${STAGE}/bdwgc/lib/libgc.a)
endif()

The make command refers to non-GNU make implementations on many systems. Please change the make command to be configurable and perhaps try to auto-detect if it is a GNU make. On some systems, GNU make is available through a binary named gmake.