make it possible to compile with -std=gnu99/c99 and use extern inlines
make it possible to compile with -std=gnu99/c99 and use extern inlines

When compiled with -std=gnu99/c99 __GNUC_GNU_INLINE__ is not defined

Signed-off-by: Peter S. Mazinger <1f4071d9f342c1637b13af9bc258f2ff72e96758@gmx.net>

groundwater/uClibc,hwoarang/uClibc,brgl/uclibc-ng,wbx-github/uclibc-ng,atgreen/uClibc-moxie,kraj/uClibc,atgreen/uClibc-moxie,hwoarang/uClibc,groundwater/uClibc,waweber/uclibc-clang,majek/uclibc-vx32,groundwater/uClibc,ffainelli/uClibc,hwoarang/uClibc,foss-xtensa/uClibc,skristiansson/uClibc-or1k,hjl-tools/uClibc,hjl-tools/uClibc,mephi42/uClibc,ysat0/uClibc,ysat0/uClibc,ddcc/klee-uclibc-0.9.33.2,mephi42/uClibc,m-labs/uclibc-lm32,groundwater/uClibc,m-labs/uclibc-lm32,ndmsystems/uClibc,foss-xtensa/uClibc,brgl/uclibc-ng,brgl/uclibc-ng,foss-for-synopsys-dwc-arc-processors/uClibc,ndmsystems/uClibc,ndmsystems/uClibc,brgl/uclibc-ng,ffainelli/uClibc,czankel/xtensa-uclibc,foss-xtensa/uClibc,waweber/uclibc-clang,foss-for-synopsys-dwc-arc-processors/uClibc,wbx-github/uclibc-ng,ysat0/uClibc,kraj/uclibc-ng,wbx-github/uclibc-ng,kraj/uClibc,hjl-tools/uClibc,ddcc/klee-uclibc-0.9.33.2,hjl-tools/uClibc,ndmsystems/uClibc,m-labs/uclibc-lm32,ddcc/klee-uclibc-0.9.33.2,kraj/uClibc,ddcc/klee-uclibc-0.9.33.2,foss-for-synopsys-dwc-arc-processors/uClibc,mephi42/uClibc,czankel/xtensa-uclibc,ysat0/uClibc,mephi42/uClibc,majek/uclibc-vx32,kraj/uClibc,waweber/uclibc-clang,czankel/xtensa-uclibc,kraj/uclibc-ng,ffainelli/uClibc,atgreen/uClibc-moxie,kraj/uclibc-ng,ffainelli/uClibc,groundwater/uClibc,hwoarang/uClibc,wbx-github/uclibc-ng,waweber/uclibc-clang,kraj/uclibc-ng,czankel/xtensa-uclibc,m-labs/uclibc-lm32,majek/uclibc-vx32,ffainelli/uClibc,majek/uclibc-vx32,skristiansson/uClibc-or1k,foss-for-synopsys-dwc-arc-processors/uClibc,atgreen/uClibc-moxie,skristiansson/uClibc-or1k,hjl-tools/uClibc,skristiansson/uClibc-or1k,foss-xtensa/uClibc