Create a make variable for all lsdump files.

This is needed so that we can embed the paths of lsdump files in a file,
in order to make lookup faster, while creating reference dumps.

Test: mm -j64 in external/libjpeg-turbo for aosp_arm64_ab;
      out/soong/make_vars-aosp_arm64_ab.mk contains
      SOONG_LSDUMP_PATHS := <list of lsdump paths>

Change-Id: I04608429e1add307cc1ee79d2f0c348fb041613c
diff --git a/cc/sabi.go b/cc/sabi.go
index ec1d246..f5a7c77 100644
--- a/cc/sabi.go
+++ b/cc/sabi.go
@@ -16,11 +16,17 @@
 
 import (
 	"strings"
+	"sync"
 
 	"android/soong/android"
 	"android/soong/cc/config"
 )
 
+var (
+	lsdumpPaths []string
+	sabiLock    sync.Mutex
+)
+
 type SAbiProperties struct {
 	CreateSAbiDumps        bool `blueprint:"mutated"`
 	ReexportedIncludeFlags []string