build: fix developer mode compilation on FreeBSD

Recent FreeBSD versions use LLVM's lld as a linker, not the GNU ld.
Their behavior slightly differs, so adapt the build system to handle
either one.

* The LLVM's linker prints "undefined symbol:" instead of
  "undefined reference to". Tweak tools/mockup.sh to also look for that
  message.

* The LLVM's linker may only print the first dozen errors (omitting
  the rest to avoid flooding the screen). tools/update-mocks.sh relies
  on getting all errors as it extracts the missing symbols' names from
  the error output and creates mocks for them. Detect if errors were
  omitted and re-run, telling the linker to not omit any. The GNU linker
  does not support -error-limit=0, so unfortunately we can't just run
  with that option unconditionally from the first attempt.

* Nit: FreeBSD's sed(1) prints "t" for "\t" instead of a horizontal tab.
  Use a verbatim tab in the command, instead of "\t" which works on
  both.

Changelog-Fixed: Developer mode compilation on FreeBSD.

tools/mockup.sh

@@ -6,9 +6,14 @@ if [ $# -eq 0 ]; then
     set -- $(while read -r LINE; do
 	case "$LINE" in
 	    *undefined\ reference\ to*)
+		# file.cc:(.text+0x10): undefined reference to `foo()'
 		LINE=${LINE#*undefined reference to \`}
 		echo "${LINE%\'*}"
 		;;
+	    *undefined\ symbol:*)
+		# ld: error: undefined symbol: foo()
+		echo "${LINE#*undefined symbol: }"
+		;;
 	    *)
 		continue
 		;;

tools/update-mocks.sh

@@ -12,20 +12,31 @@ trap 'mv $BASE.old $FILE; rm -f $BASE.*' EXIT
 START=$(grep -F -n '/* AUTOGENERATED MOCKS START */' "$FILE" | cut -d: -f1)
 END=$(grep -F -n '/* AUTOGENERATED MOCKS END */' "$FILE" | cut -d: -f1)
 
+function make_binary() {
+    $MAKE "${FILE/%.c/}" 2> "${BASE}.err" >/dev/null
+}
+
 if [ -n "$START" ]; then
     mv "$FILE" "${BASE}.old"
     echo "${FILE}:"
     head -n "$START" "${BASE}.old" > "$FILE"
     tail -n +"$END" "${BASE}.old" >> "$FILE"
     # Try to make binary.
-    if ! $MAKE "${FILE/%.c/}" 2> "${BASE}.err" >/dev/null; then
+    if ! make_binary; then
+	# Some linkers (e.g. LLVM's one) don't print all errors. If this is the
+	# case, then re-run, asking them to do so. Search for something like
+	# this in the output:
+	# ld: error: too many errors emitted, stopping now (use -error-limit=0 to see all errors)
+	if grep -q 'too many errors emitted.*-error-limit=0' "${BASE}.err"; then
+	    LDFLAGS=-Wl,-error-limit=0 make_binary || :
+	fi
 	tools/mockup.sh < "${BASE}.err" >> "${BASE}.stubs"
 	# If there are no link errors, maybe compile fail for other reason?
 	if ! grep -F -q 'Generated stub for' "${BASE}.stubs"; then
 	    cat "${BASE}.err"
 	    exit 1
 	fi
-	sed -n 's,.*Generated stub for \(.*\) .*,\t\1,p' < "${BASE}.stubs"
+	sed -n 's,.*Generated stub for \(.*\) .*,	\1,p' < "${BASE}.stubs"
 	head -n "$START" "${BASE}.old" > "$FILE"
 	cat "${BASE}.stubs" >> "$FILE"
 	tail -n +"$END" "${BASE}.old" >> "$FILE"