Fix Cantera build: Pass compiler and SDK paths to scons

The error was: "Checking for C++ header file cmath... no"
"The C++ compiler is not correctly configured (incomplete include paths)"

When running scons via venv's Python, it doesn't inherit Homebrew's
compiler environment. Solution: explicitly pass compiler and SDK paths:
- CC=#{ENV.cc}
- CXX=#{ENV.cxx}
- CFLAGS=-isysroot#{MacOS.sdk_path}
- CXXFLAGS=-isysroot#{MacOS.sdk_path}

This ensures scons can find standard C++ headers like cmath.

Author: sbryngelson

packaging/homebrew/mfc.rb

@@ -40,12 +40,17 @@ def install
 
       # Configure Cantera build
       # Run scons with the venv's Python so it can find installed packages
+      # Pass compiler and SDK paths explicitly since Homebrew's env is isolated
       system venv/"bin/python", "-m", "SCons", "build",
              "python_package=y",
              "f90_interface=n",
              "system_sundials=y",
              "system_yamlcpp=y",
              "system_fmt=n",
+             "CC=#{ENV.cc}",
+             "CXX=#{ENV.cxx}",
+             "CFLAGS=-isysroot#{MacOS.sdk_path}",
+             "CXXFLAGS=-isysroot#{MacOS.sdk_path}",
              "extra_inc_dirs=#{Formula["sundials"].opt_include}:#{Formula["yaml-cpp"].opt_include}",
              "extra_lib_dirs=#{Formula["sundials"].opt_lib}:#{Formula["yaml-cpp"].opt_lib}",
              "prefix=#{libexec}/cantera",