Chunk 1:	Change PREFIX and MANPREFIX variables
Chunk 2:	Append local (C|CXX|LD)FLAGS, use _DEFALUT SOURCE
diff -ura sfeed.old/config.mk sfeed.new/config.mk
--- sfeed.old/config.mk	2019-02-26 10:16:47.944146690 +1100
+++ sfeed.new/config.mk	2019-02-26 10:17:47.225309885 +1100
@@ -1,9 +1,9 @@
 # customize below to fit your system
 
 # paths
-PREFIX = /usr/local
-MANPREFIX = ${PREFIX}/man
-DOCPREFIX = ${PREFIX}/share/doc/sfeed
+PREFIX = /usr
+MANPREFIX = ${PREFIX}/share/man
+DOCPREFIX = ${PREFIX}/share/doc/sfeed-git
 
 # compiler and linker
 CC = cc
@@ -11,9 +11,9 @@
 RANLIB = ranlib
 
 # use system flags.
-SFEED_CFLAGS = ${CFLAGS}
-SFEED_LDFLAGS = ${LDFLAGS}
-SFEED_CPPFLAGS = -D_POSIX_C_SOURCE=200809L -D_XOPEN_SOURCE=700 -D_BSD_SOURCE
+SFEED_CFLAGS   = ${CFLAGS}
+SFEED_LDFLAGS  = ${LDFLAGS}
+SFEED_CPPFLAGS = ${CPPFLAGS} -D_POSIX_C_SOURCE=200809L -D_XOPEN_SOURCE=700 -D_DEFAULT_SOURCE
 
 # debug
 #SFEED_CFLAGS = -fstack-protector-all -O0 -g -std=c99 -Wall -Wextra -pedantic \