Add test to configure script to detect getline

Add a simple test to the configure script to detect getline.  It's not
important that the test run, just that it compiles and links without
any errors.

Signed-off-by: Jeffrey C. Ollie <jeff@ocjtech.us>

configure

@@ -126,6 +126,15 @@ EOF
     exit 1
 fi
 
+if ! gcc -o getlinetest getlinetest.c > /dev/null 2>&1
+then
+    echo "Checking for getline... No."
+    getline=-Dgetline=_notmuch_getline
+else
+    echo "Checking for getline... Yes."
+fi
+rm -f getlinetest
+
 cat <<EOF
 
 All required packages were found. You may now run the following
@@ -139,5 +148,5 @@ EOF
 # construct the Makefile.config
 cat > Makefile.config <<EOF
 prefix = /usr/local
-override CFLAGS += -DHAVE_VALGRIND=${have_valgrind} ${valgrind_flags}
+override CFLAGS += -DHAVE_VALGRIND=${have_valgrind} ${valgrind_flags} ${getline}
 EOF

getlinetest.c

@@ -0,0 +1,13 @@
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <sys/types.h>
+
+int main()
+{
+  ssize_t count = 0;
+  size_t n = 0;
+  char **lineptr = NULL;
+  FILE *stream = NULL;
+
+  count = getline(lineptr, &n, stream);
+}