Update eye func:

1. `merge` -> `optval` inside.

Author: zoziha

src/Makefile.manual

@@ -149,7 +149,8 @@ stdlib_string_type.o: stdlib_ascii.o \
 stdlib_strings.o: stdlib_ascii.o \
     stdlib_string_type.o \
 	stdlib_optval.o
-stdlib_math.o: stdlib_kinds.o
+stdlib_math.o: stdlib_kinds.o \
+    stdlib_optval.o
 stdlib_math_linspace.o: \
 	stdlib_math.o
 stdlib_math_logspace.o: \

src/stdlib_linalg.fypp

@@ -5,6 +5,7 @@ module stdlib_linalg
   !! ([Specification](../page/specs/stdlib_linalg.html))
   use stdlib_kinds, only: sp, dp, qp, &
     int8, int16, int32, int64
+  use stdlib_optval, only: optval
   implicit none
   private
 
@@ -95,7 +96,7 @@ contains
         integer :: dim2_
         integer :: i
 
-        dim2_ = merge(dim2, dim1, present(dim2))
+        dim2_ = optval(dim2, dim1)
         allocate(result(dim1, dim2_))
 
         result = 0