I do these steps and get a 'x86-64' architecture static library:
./configure --prefix=/Users/huhai/Desktop/tempout/20181009/ --disable-FEATURE --host=armv7-apple-darwin
make optnoshared
When I use 'lipo' to check the finally created library 'lib_Darwin_armv7/libpt_s.a', it shows that 'lib_Darwin_armv7/libpt_s.a is architecture: x86_64'

