Define POSIX macro to have strdup

98c38dc6d6
sets C99 as standard.

strdup() is not part of C99.

For now set `-D_POSIX_C_SOURCE=200809L` macro to have strdup() in C99.
Using `gnu99` instead would be another option.

We should take more care to use glib functions whenever possible.

Regards https://github.com/profanity-im/profanity/issues/1357

configure.ac

@@ -354,7 +354,7 @@ AC_CHECK_HEADERS([ncursesw/ncurses.h], [], [])
 AC_CHECK_HEADERS([ncurses.h], [], [])
 
 ### Default parameters
-AM_CFLAGS="-Wall -Wno-deprecated-declarations -std=c99"
+AM_CFLAGS="-Wall -Wno-deprecated-declarations -std=c99 -D_POSIX_C_SOURCE=200809L"
 AS_IF([test "x$PACKAGE_STATUS" = xdevelopment],
     [AM_CFLAGS="$AM_CFLAGS -Wunused -Werror"])
 AS_IF([test "x$PLATFORM" = xosx],