chgcentre: fix compilation error by using explicit casting (#39315)

Co-authored-by: Cristian Di Pietrantonio <cdipietrantonio@pawsey.org.au>

var/spack/repos/builtin/packages/chgcentre/main.patch

@@ -0,0 +1,11 @@
+--- a/main.cpp	2022-05-02 15:00:00 +0800
++++ b/main.cpp	2022-05-02 15:01:00 +0800
+@@ -415,7 +415,7 @@
+ 												MDirection::Ref(MDirection::J2000))();
+ 	std::vector<Muvw> uvws(antennas.size());
+ 	MEpoch time(MVEpoch(-1.0));
+-	for(unsigned row=0; row!=std::min(set.nrow(),50u); ++row)
++	for(unsigned row=0; row!=std::min(static_cast<unsigned int>(set.nrow()),50u); ++row)
+ 	{
+ 		if(fieldIdCol(row) == fieldIndex)
+ 		{

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

@@ -18,3 +18,9 @@ class Chgcentre(CMakePackage):
 
     depends_on("casacore")
     depends_on("gsl")
+
+    # this patch is required to fix a programming error that is not acceptable by
+    # latest compilers. In particular, the `std::min` function was given `int` and
+    # `unsigned int` arguments. The `int` argument is explicitly casted to `unsigned int`.
+    # This patch was created by the staff at the Pawsey Supercomputing Research Centre.
+    patch("main.patch")