Missing symbols when building shared libraries

[madebr]

When configuring DethRace with -DBUILD_SHARED_LIBS=ON -DCMAKE_POSITION_INDEPENDENT_CODE=ON,
linking fails due to missing symbols.

(eventually add -DCMAKE_EXE_LINKER_FLAGS="-Wl,--no-undefined" to emit an error on missing symbols)

/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `TrapezoidRenderPIZ2TIA_RGB_555'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `TrapezoidRenderPIZ2TIA_RGB_888'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `TrapezoidRenderPIZ2TAN'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `ScanLinePITPD64'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `TrapezoidRenderPITA'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `ScanLinePITPD1024'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `TrapezoidRenderPITA24'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `TrapezoidRenderPITIA'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `ScanLinePITIPB256_RGB_565'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `TrapezoidRenderPIZ2TA24'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `TrapezoidRenderPIZ2TIA'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `TrapezoidRenderPITAN'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `TrapezoidRenderPITIA_RGB_555'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `TrapezoidRenderPIZ2TA15'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `TrapezoidRenderPITA15'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `TrapezoidRenderPITIA_RGB_888'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `ScanLinePITIPB256_RGB_555'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `TrapezoidRenderPIZ2TA'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `ScanLinePITPD128'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `ScanLinePITPD256'
/usr/bin/ld: lib/BRender-v1.3.2/drivers/pentprim/libsoftprmf.so: undefined reference to `ScanLinePITIP256_RGB_555'

We either should disallow building shared libraries, or merge some libraries together.

note:
I had to apply this patch to fix the double definition of _BrDefaultDiagHandler in core/fw/defdiag.c and core/std/defdiag.c.

--- a/core/fw/CMakeLists.txt
+++ b/core/fw/CMakeLists.txt
@@ -75,7 +75,7 @@ set(FW_FILES
         brqsort.c
         bswap.c
         datafile.c
-        defdiag.c
+        # defdiag.c   # core/std/stddiag.c and core/fw/defdiag.c both define _BrDefaultDiagHandler
         deffile.c
         defmem.c
         devlist.c

I think the better fix is to only export public BRender symbols from the shared libraries.
This error occurs because libbrender.so exports _BrDefaultDiagHandler twice, which is not possible.