To add some informations:
In standard cbp files, there is an environment variable defined as:
<Variable name="WX_CFG" value="" />
<Add directory="$(#wx33_64.lib)/gcc_dll$(WX_CFG)
In my unified workspace/cbp files, I define a wxwidgets path as, in my case, C:\wxWidgets-3.3.1 as the base, and in a user-defined field, I have created a wx_cfg variable. If I set this variable with nothing (an empty field), the variable is eliminated after a click on the save button. It's why, as in standard cbp files, I tried to set an empty string by "". Apparently, this is the problem described by ollydbg when I use a variable as:
<Add directory="$(#WXWIDGETS)/lib/gcc_dll$(#WXWIDGETS.WX_CFG)
<sets>
<default>
<cccccc>
<DDD>
<str>
<![CDATA[]]>
</str>
</DDD>
<BBB>
<str>
<![CDATA[xxx]]>
</str>
</BBB>
<CFLAGS>
<str>
<![CDATA[]]>
</str>
</CFLAGS>
<BIN>
<str>
<![CDATA[]]>
</str>
</BIN>
<LFLAGS>
<str>
<![CDATA[]]>
</str>
</LFLAGS>
<OBJ>
<str>
<![CDATA[]]>
</str>
</OBJ>
<LIB>
<str>
<![CDATA[]]>
</str>
</LIB>
<INCLUDE>
<str>
<![CDATA[]]>
</str>
</INCLUDE>
<BASE>
<str>
<![CDATA[aaaa]]>
</str>
</BASE>
</cccccc>
You can see, I don't want to do that DDD is a user defined key, and its value is empty. While the CFLAGS is predefined key, and its value is also empty.
So, I think the solution is: using the predefined value string, for example, a value named: __EMPTY__ or just an empty string "", then in the code when we get the value, we have to check the result, and remove the __EMPTY__ or "" in the command line.