From 5791564dd934d193df771a0a7c52013e9f456aa1 Mon Sep 17 00:00:00 2001
From: Sergei Trofimovich <slyfox@gentoo.org>
Date: Tue, 21 Jan 2020 22:33:49 +0000
Subject: [PATCH] fg_gl2: fix build failure against gcc-10

On gcc-10 (and gcc-9 -fno-common) build fails as:

```
[ 31%] Linking C executable bin/Lorenz_static
/usr/bin/cmake -E cmake_link_script CMakeFiles/Lorenz_static.dir/link.txt --verbose=1
/usr/lib/ccache/bin/cc  -Wall -pedantic  -rdynamic CMakeFiles/Lorenz_static.dir/progs/demos/Lorenz/lorenz.c.o \
   -o bin/Lorenz_static  -lGLU -lGL -lm -lX11 -lXrandr -lXxf86vm -lXi -lm lib/libglut.a -lGL -lm -lX11 -lXrandr -lXxf86vm -lXi
ld: lib/libglut.a(fg_gl2.c.o):(.bss+0x0):
  multiple definition of `fghGenBuffers'; lib/libglut.a(fg_window.c.o):(.bss+0x0): first defined here
ld: lib/libglut.a(fg_gl2.c.o):(.bss+0x8):
  multiple definition of `fghDeleteBuffers'; lib/libglut.a(fg_window.c.o):(.bss+0x8): first defined here
```

Note: duplicate definition comes here from 'fg_gl2.h'.
The fix is to move declaration to a 'fg_gl2.c' file.

gcc-10 will change the default from -fcommon to fno-common:
https://gcc.gnu.org/PR85678.

The error also happens if CFLAGS=-fno-common passed explicitly.

Bug: https://bugs.gentoo.org/705840
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
---
 src/fg_gl2.c | 12 ++++++++++++
 src/fg_gl2.h | 14 +++++++-------
 2 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/freeglut/freeglut/src/fg_gl2.c b/freeglut/freeglut/src/fg_gl2.c
index 38b0acbb..f79c432a 100644
--- a/src/fg_gl2.c
+++ b/src/fg_gl2.c
@@ -27,6 +27,18 @@
 #include "fg_internal.h"
 #include "fg_gl2.h"
 
+#ifdef GL_ES_VERSION_2_0
+/* Use existing functions on GLES 2.0 */
+#else
+FGH_PFNGLGENBUFFERSPROC fghGenBuffers;
+FGH_PFNGLDELETEBUFFERSPROC fghDeleteBuffers;
+FGH_PFNGLBINDBUFFERPROC fghBindBuffer;
+FGH_PFNGLBUFFERDATAPROC fghBufferData;
+FGH_PFNGLENABLEVERTEXATTRIBARRAYPROC fghEnableVertexAttribArray;
+FGH_PFNGLDISABLEVERTEXATTRIBARRAYPROC fghDisableVertexAttribArray;
+FGH_PFNGLVERTEXATTRIBPOINTERPROC fghVertexAttribPointer;
+#endif
+
 void FGAPIENTRY glutSetVertexAttribCoord3(GLint attrib) {
   if (fgStructure.CurrentWindow != NULL)
     fgStructure.CurrentWindow->Window.attribute_v_coord = attrib;
diff --git a/freeglut/freeglut/src/fg_gl2.h b/freeglut/freeglut/src/fg_gl2.h
index ab8ba5c7..fb3d4676 100644
--- a/src/fg_gl2.h
+++ b/src/fg_gl2.h
@@ -67,13 +67,13 @@ typedef void (APIENTRY *FGH_PFNGLENABLEVERTEXATTRIBARRAYPROC) (GLuint index);
 typedef void (APIENTRY *FGH_PFNGLDISABLEVERTEXATTRIBARRAYPROC) (GLuint);
 typedef void (APIENTRY *FGH_PFNGLVERTEXATTRIBPOINTERPROC) (GLuint index, GLint size, GLenum type, GLboolean normalized, GLsizei stride, const GLvoid *pointer);
 
-FGH_PFNGLGENBUFFERSPROC fghGenBuffers;
-FGH_PFNGLDELETEBUFFERSPROC fghDeleteBuffers;
-FGH_PFNGLBINDBUFFERPROC fghBindBuffer;
-FGH_PFNGLBUFFERDATAPROC fghBufferData;
-FGH_PFNGLENABLEVERTEXATTRIBARRAYPROC fghEnableVertexAttribArray;
-FGH_PFNGLDISABLEVERTEXATTRIBARRAYPROC fghDisableVertexAttribArray;
-FGH_PFNGLVERTEXATTRIBPOINTERPROC fghVertexAttribPointer;
+extern FGH_PFNGLGENBUFFERSPROC fghGenBuffers;
+extern FGH_PFNGLDELETEBUFFERSPROC fghDeleteBuffers;
+extern FGH_PFNGLBINDBUFFERPROC fghBindBuffer;
+extern FGH_PFNGLBUFFERDATAPROC fghBufferData;
+extern FGH_PFNGLENABLEVERTEXATTRIBARRAYPROC fghEnableVertexAttribArray;
+extern FGH_PFNGLDISABLEVERTEXATTRIBARRAYPROC fghDisableVertexAttribArray;
+extern FGH_PFNGLVERTEXATTRIBPOINTERPROC fghVertexAttribPointer;
 
 #    endif