Remove explicit -msse2 flags (and some other minor things)

-msse2 is passed by default in //build's gn setup (even -mssse3 now:
https://chromium-review.googlesource.com/c/chromium/src/+/2311044),
so there's no need to pass this explicitly.

Also remove some other things that are already set elsewhere.

No intended behavior change.

Bug: chromium:1220175
Change-Id: Id49540d17e21362e5f57156b47cf49a5534d89af
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/55610
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
diff --git a/BUILD.gn b/BUILD.gn
index ed48ff6..50c16e3 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -83,7 +83,6 @@
     } else if (current_cpu == "x86") {  # 32 bit version
       cflags += [
         "-m32",
-        "-msse2",
         "-mfpmath=sse",
         "-march=pentium4",
         "-mtune=generic",
diff --git a/src/Common/BUILD.gn b/src/Common/BUILD.gn
index 8cda8a1..6b3305e 100644
--- a/src/Common/BUILD.gn
+++ b/src/Common/BUILD.gn
@@ -21,8 +21,6 @@
       "/wd4201",  # nameless struct/union
       "/wd5030",  # attribute is not recognized
     ]
-  } else if (current_cpu == "x86" || current_cpu == "x64") {
-    cflags = [ "-msse2" ]
   }
 }
 
diff --git a/src/Main/BUILD.gn b/src/Main/BUILD.gn
index 0658d66..4dac33b 100644
--- a/src/Main/BUILD.gn
+++ b/src/Main/BUILD.gn
@@ -29,10 +29,6 @@
         "-Wno-sign-compare",
       ]
     }
-  } else if (current_cpu == "x86" || current_cpu == "x64") {
-    cflags = [ "-msse2" ]
-    defines =
-        [ "NO_SANITIZE_FUNCTION=__attribute__((no_sanitize(\"function\")))" ]
   }
 }
 
diff --git a/src/Reactor/BUILD.gn b/src/Reactor/BUILD.gn
index b8093ce..afd22f1 100644
--- a/src/Reactor/BUILD.gn
+++ b/src/Reactor/BUILD.gn
@@ -26,14 +26,6 @@
     ]
   } else {
     cflags = [ "-Wno-unused-local-typedef" ]
-    defines = [
-      "__STDC_CONSTANT_MACROS",
-      "__STDC_LIMIT_MACROS",
-    ]
-
-    if (current_cpu == "x86" || current_cpu == "x64") {
-      cflags += [ "-msse2" ]
-    }
   }
 }
 
diff --git a/src/Renderer/BUILD.gn b/src/Renderer/BUILD.gn
index 364a1a1..deda918 100644
--- a/src/Renderer/BUILD.gn
+++ b/src/Renderer/BUILD.gn
@@ -23,10 +23,7 @@
       "/wd5030",  # attribute is not recognized
     ]
   } else if (current_cpu == "x86" || current_cpu == "x64") {
-    cflags = [
-      "-msse2",
-      "-Wno-sign-compare",
-    ]
+    cflags = [ "-Wno-sign-compare" ]
   }
 }
 
diff --git a/third_party/llvm-10.0/BUILD.gn b/third_party/llvm-10.0/BUILD.gn
index 9ab811c..25e84e5 100644
--- a/third_party/llvm-10.0/BUILD.gn
+++ b/third_party/llvm-10.0/BUILD.gn
@@ -70,9 +70,6 @@
       "-Wno-unused-result",
       "-Wno-unused-variable",
     ]
-    if (current_cpu == "x86" || current_cpu == "x64") {
-      cflags += [ "-msse2" ]
-    }
   }
 
   defines = [