Thanks quinq!
POSIX/quinq says:
"In the absence of options that inhibit invocation of the link editor, such as
-c or -E, the c99 utility shall cause the equivalent of a -l c option to be
passed to the link editor after the last pathname operand or -l option, causing
it to be searched after all other object files and libraries are loaded."
# includes and libs
INCS = -I${GITINC}
-LIBS = -L${GITLIB} -lgit2 -lc
+LIBS = -L${GITLIB} -lgit2
# debug
#CFLAGS = -fstack-protector-all -O0 -g -std=c99 -Wall -Wextra -pedantic ${INCS}