Install mimalloc headers in sysroot (#21699)

Author: Markus87

test/test_other.py

@@ -14596,3 +14596,14 @@ def test_use_port_errors(self, compiler):
     stderr = self.expect_fail([compiler, test_file('hello_world.c'), '--use-port=sdl2_image:formats=jpg:formats=png', '-o', 'out.js'])
     self.assertFalse(os.path.exists('out.js'))
     self.assertContained('error with `--use-port=sdl2_image:formats=jpg:formats=png` | duplicate option `formats`', stderr)
+
+  def test_mimalloc_headers(self):
+    src = r'''
+      #include <mimalloc.h>
+
+      int main() {
+          mi_option_enable(mi_option_verbose);
+          return 0;
+      }
+    '''
+    self.do_run(src, emcc_args=['-sMALLOC=mimalloc'])

tools/system_libs.py

@@ -2436,6 +2436,7 @@ def install_system_headers(stamp):
     ('lib', 'libc', 'musl', 'include'): '',
     ('lib', 'libcxx', 'include'): os.path.join('c++', 'v1'),
     ('lib', 'libcxxabi', 'include'): os.path.join('c++', 'v1'),
+    ('lib', 'mimalloc', 'include'): '',
   }
 
   target_include_dir = cache.get_include_dir()