Generated a separate 'config.h' for arm, arm_64, x86_32, x86_64 for the
current version (6.1.2) of GMP. This became necessary because
configurations differ for each architecture.
'config.h' generaton on x86_64 host in'gmp-6.1.2' directory:
for x86_64 (native):
! configure
for x86_32:
! configure --host=x86-pc-linux-gnu --build=x86_64-pc-linux-gnu
for arm:
! configure --host=arm-linux-gnu --build=x86_64-pc-linux-gnu \
! CC=/usr/local/gcc-linaro-arm/bin/arm-linux-gnueabi-gcc ABI=32
for arm_v8:
! configure --host=aarch64-linux-gnu --build=x86_64-pc-linux-gnu \
! CC=/usr/local/gcc-linaro/bin/aarch64-linux-gnu-gcc ABI=64
issue #3598
