APR_VERSION_STRING_CSV definition is malformed in apr HEAD and as far back as v1.5.1. I discovered this while attempting to build a win32 version using the mingwpy (gcc-based) toolchain. Some compilers (e.g., clang on macosx) don't fail until you actually reference the malformed definition, which is how I am guessing this malformed constant passed your builds. However, other compilers (e.g., in mingwpy toolchain) choke on it.

To reproduce, try compiling the following code sample, first as is to see how the HEAD version of the macro breaks; then comment out the first APR_VERSION_STRING_CSV definition and uncomment the second definition to see how the one from apr v1.5.1 breaks.

```c
#define APR_MAJOR_VERSION 2
#define APR_MINOR_VERSION 0
#define APR_PATCH_VERSION 0

# From apr 2.0.0
#define APR_VERSION_STRING_CSV APR_MAJOR_VERSION, \
                               APR_MINOR_VERSION, \
                               APR_PATCH_VERSION


# From apr 1.5.1; was also malformed
//#define APR_VERSION_STRING_CSV APR_MAJOR_VERSION ##, \
//                               ##APR_MINOR_VERSION ##, \
//                               ##APR_PATCH_VERSION


int main() {
    char* version = APR_VERSION_STRING_CSV;
    return 0;
}
```

The error that I got while building apr with the mingwpy toolchain was the following:

[ 97%] Building RC object CMakeFiles/libapr-1.dir/libapr.rc.obj
C:\mingwpy\bin\windres.exe  -O coff -DAPR_DECLARE_EXPORT -DWINNT -Dlibapr_1_EXPORTS -IC:\Users\Administrator\nta\nupic.c
ore\build\apr\build -IC:\Users\Administrator\nta\nupic.core\build\apr\include -IC:\Users\Administrator\nta\nupic.core\bu
ild\apr\include\arch\win32 -IC:\Users\Administrator\nta\nupic.core\build\apr\include\arch\unix -IC:\Users\Administrator\
nta\nupic.core\build\apr\include\private   C:\Users\Administrator\nta\nupic.core\build\apr\libapr.rc CMakeFiles\libapr-1
.dir\libapr.rc.obj
In file included from C:\Users\Administrator\nta\nupic.core\build\apr\libapr.rc:1:0:
C:\Users\Administrator\nta\nupic.core\build\apr\include/apr_version.h:117:32: error: pasting "APR_MAJOR_VERSION" and ","
 does not give a valid preprocessing token
 #define APR_VERSION_STRING_CSV APR_MAJOR_VERSION ##, \
                                ^
C:\Users\Administrator\nta\nupic.core\build\apr\libapr.rc:21:14: note: in expansion of macro 'APR_VERSION_STRING_CSV'
  FILEVERSION APR_VERSION_STRING_CSV,0
              ^
C:\Users\Administrator\nta\nupic.core\build\apr\include/apr_version.h:117:52: error: pasting "," and "APR_MINOR_VERSION"
 does not give a valid preprocessing token
 #define APR_VERSION_STRING_CSV APR_MAJOR_VERSION ##, \
                                                    ^
C:\Users\Administrator\nta\nupic.core\build\apr\libapr.rc:21:14: note: in expansion of macro 'APR_VERSION_STRING_CSV'
  FILEVERSION APR_VERSION_STRING_CSV,0
              ^
C:\Users\Administrator\nta\nupic.core\build\apr\include/apr_version.h:118:32: error: pasting "APR_MINOR_VERSION" and ","
 does not give a valid preprocessing token
                              ##APR_MINOR_VERSION ##, \
                                ^
C:\Users\Administrator\nta\nupic.core\build\apr\libapr.rc:21:14: note: in expansion of macro 'APR_VERSION_STRING_CSV'
  FILEVERSION APR_VERSION_STRING_CSV,0
              ^
C:\Users\Administrator\nta\nupic.core\build\apr\include/apr_version.h:118:52: error: pasting "," and "APR_PATCH_VERSION"
 does not give a valid preprocessing token
                              ##APR_MINOR_VERSION ##, \
                                                    ^
C:\Users\Administrator\nta\nupic.core\build\apr\libapr.rc:21:14: note: in expansion of macro 'APR_VERSION_STRING_CSV'
  FILEVERSION APR_VERSION_STRING_CSV,0
              ^
C:\Users\Administrator\nta\nupic.core\build\apr\include/apr_version.h:117:32: error: pasting "APR_MAJOR_VERSION" and ","
 does not give a valid preprocessing token
 #define APR_VERSION_STRING_CSV APR_MAJOR_VERSION ##, \
                                ^
C:\Users\Administrator\nta\nupic.core\build\apr\libapr.rc:22:17: note: in expansion of macro 'APR_VERSION_STRING_CSV'
  PRODUCTVERSION APR_VERSION_STRING_CSV,0
                 ^
C:\Users\Administrator\nta\nupic.core\build\apr\include/apr_version.h:117:52: error: pasting "," and "APR_MINOR_VERSION"
 does not give a valid preprocessing token
 #define APR_VERSION_STRING_CSV APR_MAJOR_VERSION ##, \
                                                    ^
C:\Users\Administrator\nta\nupic.core\build\apr\libapr.rc:22:17: note: in expansion of macro 'APR_VERSION_STRING_CSV'
  PRODUCTVERSION APR_VERSION_STRING_CSV,0
                 ^
C:\Users\Administrator\nta\nupic.core\build\apr\include/apr_version.h:118:32: error: pasting "APR_MINOR_VERSION" and ","
 does not give a valid preprocessing token
                              ##APR_MINOR_VERSION ##, \
                                ^
C:\Users\Administrator\nta\nupic.core\build\apr\libapr.rc:22:17: note: in expansion of macro 'APR_VERSION_STRING_CSV'
  PRODUCTVERSION APR_VERSION_STRING_CSV,0
                 ^
C:\Users\Administrator\nta\nupic.core\build\apr\include/apr_version.h:118:52: error: pasting "," and "APR_PATCH_VERSION"
 does not give a valid preprocessing token
                              ##APR_MINOR_VERSION ##, \
                                                    ^
C:\Users\Administrator\nta\nupic.core\build\apr\libapr.rc:22:17: note: in expansion of macro 'APR_VERSION_STRING_CSV'
  PRODUCTVERSION APR_VERSION_STRING_CSV,0
                 ^
C:\mingwpy\bin\windres.exe: preprocessing failed.