Docs, add missing `member` role for C domain

Fixes sphinx-doc/sphinx#4038

CHANGES

@@ -29,6 +29,7 @@ Bugs fixed
 * #4006: Fix crash on parallel build
 * #3969: private instance attributes causes AttributeError
 * #4041: C++, remove extra name linking in function pointers.
+* #4038: C, add missing documentation of ``member`` role.
 
 Testing
 --------

doc/domains.rst

@@ -473,7 +473,7 @@ The C Domain
 
 The C domain (name **c**) is suited for documentation of C API.
 
-.. rst:directive:: .. c:function:: type name(signature)
+.. rst:directive:: .. c:function:: function prototype
 
    Describes a C function. The signature should be given as in C, e.g.::
 
@@ -485,7 +485,7 @@ The C domain (name **c**) is suited for documentation of C API.
    Note that you don't have to backslash-escape asterisks in the signature, as
    it is not parsed by the reST inliner.
 
-.. rst:directive:: .. c:member:: type name
+.. rst:directive:: .. c:member:: declaration
 
    Describes a C struct member. Example signature::
 
@@ -508,7 +508,7 @@ The C domain (name **c**) is suited for documentation of C API.
    Describes a C type (whether defined by a typedef or struct). The signature
    should just be the type name.
 
-.. rst:directive:: .. c:var:: type name
+.. rst:directive:: .. c:var:: declaration
 
    Describes a global C variable.  The signature should include the type, such
    as::
@@ -524,14 +524,14 @@ Cross-referencing C constructs
 The following roles create cross-references to C-language constructs if they are
 defined in the documentation:
 
-.. rst:role:: c:data
-
-   Reference a C-language variable.
-
 .. rst:role:: c:func
 
    Reference a C-language function. Should include trailing parentheses.
 
+.. rst:role:: c:member
+
+   Reference a C-language member of a struct.
+
 .. rst:role:: c:macro
 
    Reference a "simple" C macro, as defined above.
@@ -540,6 +540,10 @@ defined in the documentation:
 
    Reference a C-language type.
 
+.. rst:role:: c:data
+
+   Reference a C-language variable.
+
 
 The C++ Domain
 --------------