Seems to be a (recent - 7.55.X ?) change to Makefile generation.

I did this

git clone ...
./buildconf
./configure ...

I expected the following

curl to build

I get

• make > .buildaix/make.out
  "Makefile", line 3808: make: 1254-055 Dependency line needs colon or double colon operator.
  "Makefile", line 3809: make: 1254-055 Dependency line needs colon or double colon operator.
  "Makefile", line 3810: make: 1254-055 Dependency line needs colon or double colon operator.

My hack

a) delete all lines after .PRECIOUS: Makefile
b) comment all lines with either ?= or +=

curl/libcurl version

7.57.0-DEV

operating system

AIX 5.3 TL7, AIX 6.1 TL9