Fixed Linux build.

src/image.cpp

@@ -5,6 +5,7 @@
 
 #include "bgfx_p.h"
 #include <bx/float4_t.h>
+#include <math.h> // powf
 
 namespace bgfx
 {

tools/texturec/texturec.cpp

@@ -31,7 +31,7 @@ namespace bgfx
 		return mem;
 	}
 
-	void saveTga(const char* _filePath, uint32_t _width, uint32_t _height, uint32_t _srcPitch, const void* _src, bool _grayscale, bool _yflip)
+	void saveTga(const char* _filePath, uint32_t _width, uint32_t _height, uint32_t _srcPitch, const void* _src, bool _grayscale = false, bool _yflip = false)
 	{
 		FILE* file = fopen(_filePath, "wb");
 		if ( NULL != file )