the current Go doesn’t support c-shared on other architectures than amd64

same for LDFLAGS. this fixes common problem where CFLAGS after make
was evaluated as a make variable and replaced the default, while
before as env variable and was prepended to the default string.
now they both behave as an env. variable

this also fixes static linking missing a math library

This reverts commit 3f4d8cbe.

this saves space for both library and daemon

Headers were installed with executable flag set on Linux.

the build system now doesn't always relink targets