Revert of win: Remove unneeded references to visual_studio_version now that it's always 2015. (patchset #4 id:60001 of https://codereview.chromium.org/2450933002/ )

Reason for revert:
V8 relies on this.

Original issue's description:
> win: Remove unneeded references to visual_studio_version now that it's always 2015.
>
> BUG=
>
> Committed: https://crrev.com/a628db5056deb88589224bd68dcd9ec029932c83
> Cr-Commit-Position: refs/heads/master@{#427463}

TBR=scottmg@chromium.org,thakis@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=

Review-Url: https://codereview.chromium.org/2531333004
Cr-Original-Commit-Position: refs/heads/master@{#434945}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: f89b499961b139f38e8e01282a82d4ba5d21506e

config/compiler/BUILD.gn

@@ -17,6 +17,9 @@ if (current_cpu == "arm" || current_cpu == "arm64") {
 if (current_cpu == "mipsel" || current_cpu == "mips64el") {
   import("//build/config/mips.gni")
 }
+if (is_win) {
+  import("//build/config/win/visual_studio_version.gni")
+}
 if (is_mac) {
   import("//build/config/mac/symbols.gni")
 }
@@ -909,20 +912,22 @@ config("default_warnings") {
       "/wd4459",
     ]
 
-    cflags += [
-      # C4312 is a VS 2015 64-bit warning for integer to larger pointer.
-      # TODO(brucedawson): fix warnings, crbug.com/554200
-      "/wd4312",
-    ]
-
-    if (current_cpu == "x86") {
+    if (visual_studio_version == "2015") {
       cflags += [
-        # VC++ 2015 changes 32-bit size_t truncation warnings from 4244 to
-        # 4267. Example: short TruncTest(size_t x) { return x; }
-        # Since we disable 4244 we need to disable 4267 during migration.
-        # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
-        "/wd4267",
+        # C4312 is a VS 2015 64-bit warning for integer to larger pointer.
+        # TODO(brucedawson): fix warnings, crbug.com/554200
+        "/wd4312",
       ]
+
+      if (current_cpu == "x86") {
+        cflags += [
+          # VC++ 2015 changes 32-bit size_t truncation warnings from 4244 to
+          # 4267. Example: short TruncTest(size_t x) { return x; }
+          # Since we disable 4244 we need to disable 4267 during migration.
+          # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
+          "/wd4267",
+        ]
+      }
     }
 
     # VS xtree header file needs to be patched or 4702 (unreachable code
@@ -935,6 +940,7 @@ config("default_warnings") {
 
     # Building with Clang on Windows is a work in progress and very
     # experimental. See crbug.com/82385.
+    # Keep this in sync with the similar block in build/common.gypi
     if (is_clang) {
       cflags += [
         # TODO(hans): Make this list shorter eventually, http://crbug.com/504657
@@ -1544,7 +1550,7 @@ config("symbols") {
     import("//build/toolchain/goma.gni")
     cflags = [ "/Zi" ]  # Produce PDB file, no edit and continue.
 
-    if (is_win_fastlink) {
+    if (is_win_fastlink && visual_studio_version != "2013") {
       # Tell VS 2015+ to create a PDB that references debug
       # information in .obj and .lib files instead of copying
       # it all. This flag is incompatible with /PROFILE

config/win/BUILD.gn

@@ -48,24 +48,36 @@ config("compiler") {
   cflags_c = [ "/TC" ]
   cflags_cc = [ "/TP" ]
 
-  cflags += [
-    # Tell the compiler to crash on failures. This is undocumented
-    # and unsupported but very handy.
-    "/d2FastFail",
+  # Flags not supported in version 2013.
+  if (visual_studio_version != "2013" && visual_studio_version != "2013e") {
+    cflags += [
+      # Tell the compiler to crash on failures. This is undocumented
+      # and unsupported but very handy.
+      "/d2FastFail",
+    ]
+  }
 
-    # Work around crbug.com/526851, bug in VS 2015 RTM compiler.
-    "/Zc:sizedDealloc-",
+  if (visual_studio_version == "2015") {
+    cflags += [
+      # Work around crbug.com/526851, bug in VS 2015 RTM compiler.
+      "/Zc:sizedDealloc-",
 
-    # Disable thread-safe statics to avoid overhead and because
-    # they are disabled on other platforms. See crbug.com/587210
-    # and -fno-threadsafe-statics.
-    "/Zc:threadSafeInit-",
-  ]
+      # Disable thread-safe statics to avoid overhead and because
+      # they are disabled on other platforms. See crbug.com/587210
+      # and -fno-threadsafe-statics.
+      "/Zc:threadSafeInit-",
+    ]
+  }
 
   # Building with Clang on Windows is a work in progress and very
   # experimental. See crbug.com/82385.
+  # Keep this in sync with the similar block in build/common.gypi
   if (is_clang) {
-    cflags += [ "-fmsc-version=1900" ]
+    if (visual_studio_version == "2013") {
+      cflags += [ "-fmsc-version=1800" ]
+    } else if (visual_studio_version == "2015") {
+      cflags += [ "-fmsc-version=1900" ]
+    }
 
     if (current_cpu == "x86") {
       cflags += [ "-m32" ]

config/win/visual_studio_version.gni

@@ -9,7 +9,7 @@ declare_args() {
   visual_studio_path = ""
 
   # Version of Visual Studio pointed to by the visual_studio_path.
-  # Currently always "2015".
+  # Use "2013" for Visual Studio 2013, or "2013e" for the Express version.
   visual_studio_version = ""
 
   # Directory of the Windows driver kit. If visual_studio_path is empty, this