Fix typos in build files for msmap2tsv, handoff.

R=erikchen@chromium.org, rockot@chromium.org
TBR=erikchen@chromium.org, rockot@chromium.org

Review URL: https://codereview.chromium.org/950043003

Cr-Commit-Position: refs/heads/master@{#317694}

components/handoff/BUILD.gn

@@ -4,7 +4,7 @@
 
 source_set("handoff") {
   if (is_mac || is_ios) {
-    sources += [
+    sources = [
       "handoff_utility.h",
       "handoff_utility.mm",
     ]

third_party/codesighs/BUILD.gn

@@ -28,7 +28,7 @@ if (is_win) {
       "msmap2tsv.c",
     ]
 
-    libs += [ "dbghelp.lib" ]
+    libs = [ "dbghelp.lib" ]
 
     configs -= [ "//build/config/compiler:chromium_code" ]
     configs += [ "//build/config/compiler:no_chromium_code" ]