[build] Add --ldflags to _build/oils.sh

Based on Zulip feedback.

build/ninja_main.py

@@ -208,7 +208,7 @@ def ShellFunctions(cc_sources, f, argv0):
 
     print('  echo "LINK $out"', file=f)
     # note: can't have spaces in filenames
-    print('  link "$compiler" "$variant" "" "$out" \\', file=f)
+    print('  link "$compiler" "$variant" "$FLAG_ldflags" "$out" \\', file=f)
     # put each object on its own line, and indent by 4
     print('    %s' % (' \\\n    '.join(objects)), file=f)
     print('', file=f)

build/oils-preamble.sh

@@ -24,6 +24,9 @@ Flags:
   --variant ARG [default 'opt']
     The build variant, e.g. dbg, opt, asan
 
+  --ldflags LDFLAGS [default '']
+    Space-separated list of additional linker flags.
+
   --translator ARG [default 'mycpp']
     Which bundle of translated source code to compile: mycpp, mycpp-souffle
 
@@ -42,6 +45,7 @@ EOF
 
 FLAG_cxx=cxx           # default is system compiler
 FLAG_variant=opt       # default is optimized build
+FLAG_ldflags=          # default is no flags
 
 FLAG_translator=mycpp  # or mycpp-souffle
 FLAG_skip_rebuild=''   # false
@@ -69,6 +73,14 @@ parse_flags() {
         FLAG_cxx=$1
         ;;
 
+      --ldflags)
+        if test $# -eq 1; then
+          die "--ldflags requires an argument"
+        fi
+        shift
+        FLAG_ldflags=$1
+        ;;
+
       --variant)
         if test $# -eq 1; then
           die "--variant requires an argument"