arm: build: Support ARM build without FPU

src/build/config/arm.gni

@@ -28,6 +28,8 @@ if (current_cpu == "arm" || v8_current_cpu == "arm") {
     arm_use_thumb = true
 
     arm_cpu = ""
+    arm_fpu = ""
+    arm_use_neon = ""
   }
 
   if (current_os == "android" || target_os == "android") {
@@ -43,6 +45,10 @@ if (current_cpu == "arm" || v8_current_cpu == "arm") {
   assert(arm_float_abi == "" || arm_float_abi == "hard" ||
          arm_float_abi == "soft" || arm_float_abi == "softfp")
 
+  if (arm_use_neon == "") {
+    arm_use_neon = false
+  }
+
   if (arm_version == 6) {
     assert(false, "arm_version must be >= 7")
   } else if (arm_version == 7) {
@@ -58,6 +64,14 @@ if (current_cpu == "arm" || v8_current_cpu == "arm") {
         arm_float_abi = "hard"
       }
     }
+
+    if (arm_fpu == "") {
+      if (arm_use_neon) {
+        arm_fpu = "neon"
+      } else {
+        arm_fpu = "vfpv3-d16"
+      }
+    }
   } else if (arm_version == 8) {
     if (arm_arch == "") {
       arm_arch = "armv8-a"
@@ -65,11 +79,20 @@ if (current_cpu == "arm" || v8_current_cpu == "arm") {
     if (arm_float_abi == "") {
       arm_float_abi = "hard"
     }
+
+    if (arm_fpu == "") {
+      if (arm_use_neon) {
+        arm_fpu = "neon"
+      } else {
+        arm_fpu = "vfpv3-d16"
+      }
+    }
   }
 } else if (current_cpu == "arm64" || v8_current_cpu == "arm64" ||
            current_cpu == "arm64e" || v8_current_cpu == "arm64e") {
   # arm64 supports only "hard".
   arm_float_abi = "hard"
+  arm_use_neon = true
   declare_args() {
     arm_cpu = ""
   }

src/build/config/compiler/BUILD.gn

@@ -1625,8 +1625,8 @@ config("rustc_revision") {
 }
 
 config("compiler_arm_fpu") {
-  if (current_cpu == "arm" && !is_ios) {
-    cflags = [ "-mfpu=neon" ]
+  if (current_cpu == "arm" && !is_ios && arm_fpu != "") {
+    cflags = [ "-mfpu=$arm_fpu" ]
     if (!arm_use_thumb) {
       cflags += [ "-marm" ]
     }

src/third_party/zlib/BUILD.gn

@@ -70,7 +70,7 @@ source_set("zlib_common_headers") {
 # TODO(ritownsend@google.com): Optimizations temporarily disabled for
 # Windows on Arm MSVC builds, see http://crbug.com/v8/10012.
 use_arm_neon_optimizations =
-    (current_cpu == "arm" || current_cpu == "arm64") && !(is_win && !is_clang)
+    (current_cpu == "arm" || current_cpu == "arm64") && !(is_win && !is_clang) && arm_use_neon
 
 use_x86_x64_optimizations =
     (current_cpu == "x86" || current_cpu == "x64") && !is_ios