Add Python chmod +x equivalent in fpm package (#30342)

var/spack/repos/builtin/packages/fpm/package.py

@@ -3,6 +3,9 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
+import os
+import stat
+
 from spack import *
 
 
@@ -52,7 +55,12 @@ def install(self, spec, prefix):
         This functionality is provided by the ``install.sh`` script.
         """
 
-        script = Executable("./install.sh")
+        # Perform `chmod +x ./install.sh`
+        script_path = './install.sh'
+        st = os.stat(script_path)
+        os.chmod(script_path, st.st_mode | stat.S_IXUSR)
+
+        script = Executable(script_path)
         script(*self.install_args())
 
     def install_args(self):