gn2bp: parse cpp_std from cflags

Chromium is using both c++20 and c++17 (though all of //base:base seems
to use c++20).

Test: //base:base
Change-Id: Ibda3b67e3745d7eda56f260ae8c065512c1f672b
diff --git a/tools/gn2bp/Android.bp.swp b/tools/gn2bp/Android.bp.swp
index 739b2b1..1f88b45 100644
--- a/tools/gn2bp/Android.bp.swp
+++ b/tools/gn2bp/Android.bp.swp
@@ -219,6 +219,7 @@
     header_libs: [
         "jni_headers",
     ],
+    cpp_std: "c++20",
 }
 
 // GN: //base/allocator/partition_allocator:partition_alloc_buildflags
@@ -968,6 +969,7 @@
     header_libs: [
         "jni_headers",
     ],
+    cpp_std: "c++20",
 }
 
 // GN: //base:base_jni_headers
@@ -1274,6 +1276,7 @@
     header_libs: [
         "jni_headers",
     ],
+    cpp_std: "c++20",
 }
 
 // GN: //base:build_date
@@ -1595,6 +1598,7 @@
     header_libs: [
         "jni_headers",
     ],
+    cpp_std: "c++20",
 }
 
 // GN: //base/third_party/dynamic_annotations:dynamic_annotations
@@ -1629,6 +1633,7 @@
     header_libs: [
         "jni_headers",
     ],
+    cpp_std: "c++20",
 }
 
 // GN: //base:tracing_buildflags
@@ -2822,6 +2827,7 @@
     header_libs: [
         "jni_headers",
     ],
+    cpp_std: "c++20",
 }
 
 // GN: //third_party/boringssl:boringssl_asm
@@ -2880,6 +2886,7 @@
     header_libs: [
         "jni_headers",
     ],
+    cpp_std: "c++20",
 }
 
 // GN: //third_party/icu:icuuc_private
@@ -2931,6 +2938,7 @@
     header_libs: [
         "jni_headers",
     ],
+    cpp_std: "c++20",
 }
 
 // GN: //third_party/icu:icuuc_public
@@ -2985,6 +2993,7 @@
     header_libs: [
         "jni_headers",
     ],
+    cpp_std: "c++20",
 }
 
 // GN: //third_party/modp_b64:modp_b64
@@ -3021,5 +3030,6 @@
     header_libs: [
         "jni_headers",
     ],
+    cpp_std: "c++20",
 }