Add patch to fix chemistry-disabled build

MFC's CMakeLists.txt sets -D chemistry=False by default, but
m_derived_types.fpp unconditionally tries to use m_thermochem
module (which is only generated when chemistry is enabled via
mfc.sh, not in standalone CMake builds).

Fix:
- Patch m_derived_types.fpp to conditionally import m_thermochem
- Define stub num_species=1 when chemistry=False
- Apply patch to both v5.1.0 and master versions
- Remove parallel=False (no longer needed with this fix)
- Document patch in SPACK.md

Author: sbryngelson

packaging/spack/SPACK.md

@@ -146,6 +146,11 @@ The package configures the build environment:
 - Sets up compiler wrappers for MPI when enabled
 - Configures GPU toolchains when GPU variants are selected
 
+### Patches
+
+The package includes patches to fix build issues:
+- `fix-chemistry-disabled.patch`: Fixes CMake-only builds by providing a stub `num_species` parameter when chemistry support is disabled (default for CMake builds). This allows `m_derived_types` to compile without requiring the generated `m_thermochem` module.
+
 ### CMake Integration
 
 Spack automatically handles CMake configuration:

packaging/spack/fix-chemistry-disabled.patch

@@ -0,0 +1,21 @@
+diff --git a/src/common/m_derived_types.fpp b/src/common/m_derived_types.fpp
+index 1234567..7654321 100644
+--- a/src/common/m_derived_types.fpp
++++ b/src/common/m_derived_types.fpp
+@@ -11,10 +11,16 @@ module m_derived_types
+     use m_constants  !< Constants
+ 
+     use m_precision_select
++#:if chemistry
+     use m_thermochem, only: num_species
++#:else
++    ! Chemistry disabled: use dummy value for num_species
++    integer, parameter :: num_species = 1
++#:endif
+ 
+     implicit none
+ 
+     !> Derived type adding the field position (fp) as an attribute
+     type field_position
+         real(wp), allocatable, dimension(:, :, :) :: fp !< Field position
+

packaging/spack/package.py

@@ -25,6 +25,9 @@ class Mfc(CMakePackage):
     version("master", branch="master")
     version("5.1.0", sha256="4684bee6a529287f243f8929fb7edb0dfebbb04df7c1806459761c9a6c9261cf")
 
+    # Patches
+    patch("fix-chemistry-disabled.patch", when="@5.1.0,master")
+
     # Build options
     variant("mpi", default=True, description="Build with MPI support")
     variant("openacc", default=False, description="Build with OpenACC GPU support")