Add a premake message when Xcode command line tools isn't installed

Diffs=
949c70600 Add a premake message when Xcode command line tools isn't installed (#7756)

Co-authored-by: Chris Dalton <99840794+csmartdalton@users.noreply.github.com>

.rive_head

diff --git a/.rive_head b/.rive_head
index b080470..17eacd6 100644
--- a/.rive_head
+++ b/.rive_head
@@ -1 +1 @@
-4bf7c75453f0fc3fec1519a9a3dfe7a4ed63a054
+949c70600a6c30bfe3ef6e59685235407af1a323

build/rive_build_config.lua

diff --git a/build/rive_build_config.lua b/build/rive_build_config.lua
index 8396eeb..cfac708 100644
--- a/build/rive_build_config.lua
+++ b/build/rive_build_config.lua
@@ -396,7 +396,14 @@
 
 if os.host() == 'macosx' 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.')
+    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.')
+    end
 
     filter('system:ios')
     do