int foo1();
int foo2(int a);

#ifndef INTEGRATION_FACADE_H
#define INTEGRATION_FACADE_H
int foo1() { return 1; }
int foo2(int a) { return a; }
#endif // INTEGRATION_FACADE_H

-------------- Build: Release in Zoog.Integration.Test.Static_Library (compiler: GNU GCC Compiler)---------------

mingw32-gcc.exe -Wall -O2 -std=gnu99 -IC:Librarygtkincludegtk-3.0 -   IC:Librarygtkincludegdk-pixbuf-2.0 -IC:Librarygtkincludeglib-2.0 -IC:Librarygtkincludepango-1.0 -IC:Librarygtklibgtk-3.03.0.0 -IC:Librarygtklibgtk-3.0 -IC:Librarygtklibglib-2.0include -IC:Librarygtkincludecairo -IC:Librarygtkincludeatk-1.0 -I"E:WorkNabusVPNClient_CrossProjectvpnopenvpn buildinclude" -c E:!WorkNabusVPNClient_CrossProjectvpnZoog.Integration.Test.Static_Libraryintegration_facade.c -o objReleaseintegration_facade.o
cmd /c if exist binReleaselibZoog.Integration.Test.a del binReleaselibZoog.Integration.Test.a
ar.exe -r -s binReleaselibZoog.Integration.Test.a objReleaseintegration_facade.o
ar.exe: creating binReleaselibZoog.Integration.Test.a
Output file is binReleaselibZoog.Integration.Test.a with size 748.00 bytes
Process terminated with status 0 (0 minute(s), 7 second(s))
0 error(s), 0 warning(s) (0 minute(s), 7 second(s))

#include "integration_facade.h"
void main()
{

    int a ;

    a = foo1();
    a = foo2(400);
}

/OUT:"E:hostReleasehost.exe" /MANIFEST /LTCG /NXCOMPAT /PDB:"E:hostReleasehost.pdb" /DYNAMICBASE "E:hostlibZoog.Integration.Test.Static_Library.lib" "kernel32.lib" "user32.lib" "gdi32.lib" "winspool.lib" "comdlg32.lib" "advapi32.lib" "shell32.lib" "ole32.lib" "oleaut32.lib" "uuid.lib" "odbc32.lib" "odbccp32.lib" /ALLOWISOLATION /DEBUG /MACHINE:X86 /OPT:REF /SAFESEH:NO /PGD:"E:hostReleasehost.pgd" /MANIFESTUAC:"level='asInvoker' uiAccess='false'" /ManifestFile:"Releasehost.exe.intermediate.manifest" /OPT:ICF /ERRORREPORT:PROMPT /NOLOGO /TLBID:1

1 > ------ Build started : Project : host, Configuration : Release Win32 ------
1 > main.c
1 > main.obj: error LNK2001: unresolved external symbol "_foo2"
1 > main.obj: error LNK2001: unresolved external symbol "_foo1"