search for ios sysroot only when necessary

Addresses this: https://2dimensions.slack.com/archives/C07HMC68S4Q/p1730237272184439

Diffs=
bdb9eb01db search for ios sysroot only when necessary (#8437)

Co-authored-by: Erik Uggeldahl <erik@rive.app>
Co-authored-by: Luigi Rosso <luigi-rosso@users.noreply.github.com>

.rive_head

@@ -1 +1 @@
-91d092f4fc0c536e65dcfc513252d7f2b159ec77
+bdb9eb01db0e9aac7a22708e72576c301cc071dc

build/rive_build_config.lua

@@ -458,27 +458,22 @@ end
 
 filter({})
 
-if os.host() == 'macosx' then
+if _OPTIONS['os'] == 'ios' then
     iphoneos_sysroot = os.outputof('xcrun --sdk iphoneos --show-sdk-path')
     if iphoneos_sysroot == nil then
         error(
-            'Unable to locate iphoneos sdk. Please ensure Xcode Command Line Tools are installed.'
+            'Unable to locate iPhoneOS SDK. Please ensure Xcode and its iOS component are installed. Additionally, ensure Xcode Command Line Tools are pointing to that Xcode location with `xcode-select -p`.'
         )
     end
 
     iphonesimulator_sysroot = os.outputof('xcrun --sdk iphonesimulator --show-sdk-path')
     if iphonesimulator_sysroot == nil then
         error(
-            'Unable to locate iphonesimulator sdk. Please ensure Xcode Command Line Tools are installed.'
+            'Unable to locate iPhone simulator SDK. Please ensure Xcode and its iOS component are installed.  Additionally, ensure Xcode Command Line Tools are pointing to that Xcode location with `xcode-select -p`.'
         )
     end
 
-    filter('system:ios')
-    do
-        buildoptions({ '-fembed-bitcode ' })
-    end
-
-    filter({ 'system:ios', 'options:variant=system' })
+    filter('options:variant=system')
     do
         buildoptions({
             '--target=arm64-apple-ios13.0.0',
@@ -487,7 +482,7 @@ if os.host() == 'macosx' then
         })
     end
 
-    filter({ 'system:ios', 'options:variant=emulator' })
+    filter('options:variant=emulator')
     do
         buildoptions({
             '--target=arm64-apple-ios13.0.0-simulator',
@@ -496,6 +491,15 @@ if os.host() == 'macosx' then
         })
     end
 
+    filter({})
+end
+
+if os.host() == 'macosx' then
+    filter('system:ios')
+    do
+        buildoptions({ '-fembed-bitcode ' })
+    end
+
     filter('system:macosx or system:ios')
     do
         buildoptions({ '-fobjc-arc' })