Use `Er' variable to define first column width in ERRORS section.

lib/libc/compat-43/sigvec.2

@@ -263,7 +263,7 @@ is set to indicated the reason.
 .Fn Sigvec
 will fail and no new signal handler will be installed if one
 of the following occurs:
-.Bl -tag -width [EINVAL]
+.Bl -tag -width Er
 .It Bq Er EFAULT
 Either
 .Fa vec

lib/libc/stdlib/atexit.3

@@ -65,7 +65,7 @@ and more are allowed as long as sufficient memory can be allocated.
 .Sh RETURN VALUES
 .Rv -std atexit
 .Sh ERRORS
-.Bl -tag -width [ENOMEM]
+.Bl -tag -width Er
 .It Bq Er ENOMEM
 No memory was available to add the function to the list.
 The existing list of functions is unmodified.

lib/libc/stdlib/getenv.3

@@ -123,7 +123,7 @@ return zero if successful; otherwise the global variable
 is set to indicate the error and a
 \-1 is returned.
 .Sh ERRORS
-.Bl -tag -width [ENOMEM]
+.Bl -tag -width Er
 .It Bq Er ENOMEM
 The function
 .Fn setenv

lib/libc/stdlib/strtod.3

@@ -99,7 +99,7 @@ returned and
 is stored in 
 .Va errno .
 .Sh ERRORS
-.Bl -tag -width [ERANGE]
+.Bl -tag -width Er
 .It Bq Er ERANGE
 Overflow or underflow occurred.
 .Sh SEE ALSO

lib/libc/stdlib/strtol.3

@@ -151,7 +151,7 @@ In both cases,
 is set to
 .Er ERANGE .
 .Sh ERRORS
-.Bl -tag -width [ERANGE]
+.Bl -tag -width Er
 .It Bq Er ERANGE
 The given string was out of range; the value converted has been clamped.
 .El

lib/libc/stdlib/strtoul.3

@@ -150,7 +150,7 @@ and sets the global variable
 to
 .Er ERANGE .
 .Sh ERRORS
-.Bl -tag -width [ERANGE]
+.Bl -tag -width Er
 .It Bq Er ERANGE
 The given string was out of range; the value converted has been clamped.
 .El