Make codec options externally configurable and remove BC7 support

This change makes it possible to exclude formats using compile time
options. BC7 is *never* exposed on the web and it has an absolutely huge
coding table which means we're just wasting space.

basis_transcoder.js 58707
basis_transcoder.wasm 224404

transcoder/basisu_transcoder.cpp

@@ -23,11 +23,25 @@
 // Set to 1 for fuzz testing. This will disable all CRC16 checks on headers and compressed data.
 #define BASISU_NO_HEADER_OR_DATA_CRC16_CHECKS 0
 
-#define BASISD_SUPPORT_DXT1			1
-#define BASISD_SUPPORT_DXT5A			1
-#define BASISD_SUPPORT_BC7				1
-#define BASISD_SUPPORT_PVRTC1			1
-#define BASISD_SUPPORT_ETC2_EAC_A8	1
+#ifndef BASISD_SUPPORT_DXT1
+#define BASISD_SUPPORT_DXT1 1
+#endif
+
+#ifndef BASISD_SUPPORT_DXT5A
+#define BASISD_SUPPORT_DXT5A 1
+#endif
+
+#ifndef BASISD_SUPPORT_BC7
+#define BASISD_SUPPORT_BC7 1
+#endif
+
+#ifndef BASISD_SUPPORT_PVRTC1
+#define BASISD_SUPPORT_PVRTC1 1
+#endif
+
+#ifndef BASISD_SUPPORT_ETC2_EAC_A8
+#define BASISD_SUPPORT_ETC2_EAC_A8 1
+#endif
 
 #define BASISD_WRITE_NEW_BC7_TABLES				0
 #define BASISD_WRITE_NEW_DXT1_TABLES			0

webgl/transcoder/CMakeLists.txt

@@ -15,5 +15,5 @@ if (EMSCRIPTEN)
   set_target_properties(basis_transcoder.js PROPERTIES
       OUTPUT_NAME "basis_transcoder"
       SUFFIX ".js"
-      LINK_FLAGS "--bind -s ALLOW_MEMORY_GROWTH=1 -O3 -s ASSERTIONS=0 -DNDEBUG")
+      LINK_FLAGS "--bind -s ALLOW_MEMORY_GROWTH=1 -O3 -s ASSERTIONS=0 -DNDEBUG -DBASISD_SUPPORT_BC7=0")
 endif()