The source file didn't include the generated config.h file. Compilation failed for me like so:
libtool: link: x86_64-cros-linux-gnu-clang -O2 -pipe -O2 -pipe -march=x86-64 -msse3 -g -fno-exceptions -fno-unwind-tables -fno-asynchronous-unwind-tables -clang-syntax -Wall -Wcast-align -Wshadow -Wstrict-prototypes -Wpointer-arith -fPIC -DPIC -Wl,-O1 -Wl,-O2 -Wl,--as-needed -o pipeconnect pipeconnect.o ../src/.libs/libassuan.so -lgpg-error -Wl,-rpath -Wl,/build/amd64-generic/tmp/portage/dev-libs/libassuan-2.4.3-r1/work/libassuan-2.4.3/src/.libs
In file included from fdpassing.c:31:
./common.h:220:1: error: redeclaration of 'stpcpy' must have the 'overloadable' attribute
__stpcpy (char *a,const char *b)
^
./common.h:217:19: note: expanded from macro '__stpcpy'
# define __stpcpy stpcpy
^
../../../../../../../usr/include/string.h:581:14: note: previous overload of function is here
extern char *stpcpy (char *__restrict __dest, const char *__restrict __src)
^
1 error generated.