Add comments on handling of zero-sized B matrix in ?GELSY (Reference-LAPACK PR 833) (#4056)

* Add comment related to zero-sized matrix B

lapack-netlib/SRC/cgelsy.f

@@ -116,6 +116,7 @@
 *>          B is COMPLEX array, dimension (LDB,NRHS)
 *>          On entry, the M-by-NRHS right hand side matrix B.
 *>          On exit, the N-by-NRHS solution matrix X.
+*>          If M = 0 or N = 0, B is not referenced.
 *> \endverbatim
 *>
 *> \param[in] LDB
@@ -148,6 +149,7 @@
 *>          The effective rank of A, i.e., the order of the submatrix
 *>          R11.  This is the same as the order of the submatrix T11
 *>          in the complete orthogonal factorization of A.
+*>          If NRHS = 0, RANK = 0 on output.
 *> \endverbatim
 *>
 *> \param[out] WORK

lapack-netlib/SRC/dgelsy.f

@@ -115,6 +115,7 @@
 *>          B is DOUBLE PRECISION array, dimension (LDB,NRHS)
 *>          On entry, the M-by-NRHS right hand side matrix B.
 *>          On exit, the N-by-NRHS solution matrix X.
+*>          If M = 0 or N = 0, B is not referenced.
 *> \endverbatim
 *>
 *> \param[in] LDB
@@ -147,6 +148,7 @@
 *>          The effective rank of A, i.e., the order of the submatrix
 *>          R11.  This is the same as the order of the submatrix T11
 *>          in the complete orthogonal factorization of A.
+*>          If NRHS = 0, RANK = 0 on output.
 *> \endverbatim
 *>
 *> \param[out] WORK

lapack-netlib/SRC/sgelsy.f

@@ -115,6 +115,7 @@
 *>          B is REAL array, dimension (LDB,NRHS)
 *>          On entry, the M-by-NRHS right hand side matrix B.
 *>          On exit, the N-by-NRHS solution matrix X.
+*>          If M = 0 or N = 0, B is not referenced.
 *> \endverbatim
 *>
 *> \param[in] LDB
@@ -147,6 +148,7 @@
 *>          The effective rank of A, i.e., the order of the submatrix
 *>          R11.  This is the same as the order of the submatrix T11
 *>          in the complete orthogonal factorization of A.
+*>          If NRHS = 0, RANK = 0 on output.
 *> \endverbatim
 *>
 *> \param[out] WORK

lapack-netlib/SRC/zgelsy.f

@@ -116,6 +116,7 @@
 *>          B is COMPLEX*16 array, dimension (LDB,NRHS)
 *>          On entry, the M-by-NRHS right hand side matrix B.
 *>          On exit, the N-by-NRHS solution matrix X.
+*>          If M = 0 or N = 0, B is not referenced.
 *> \endverbatim
 *>
 *> \param[in] LDB
@@ -148,6 +149,7 @@
 *>          The effective rank of A, i.e., the order of the submatrix
 *>          R11.  This is the same as the order of the submatrix T11
 *>          in the complete orthogonal factorization of A.
+*>          If NRHS = 0, RANK = 0 on output.
 *> \endverbatim
 *>
 *> \param[out] WORK