Version 7.29.0 uses Makefiles generated with a newer version of the autotools than the previous 7.28.1. These Makefiles try to install e.g. header files by calling install-sh with multiple source files as arguments. The bundled install-sh is to old and does not support this.
The problem only occurs, if install-sh is actually being used, ie. the platform install executable is to old or not usable. Example: Solaris 10.
either update install-sh in the curl base directory. The file can e.g. be taken out of a recent uatomake installation.
or overwrite the install-sh with the one coming with automake during automake run by adding force flags in buildconf.
Files which currently get not installed correct are most include header files and man3 man pages. After updating install-sh another "make install" correctly installs all files.