Remove glslang.m4

The m4 grammar build mechanism was only ever needed as a preprocessor
for bison, to be used with GLSLANG_WEB, which has now been removed.

Fixes #2958

glslang/CMakeLists.txt

@@ -57,7 +57,6 @@ set_property(TARGET GenericCodeGen PROPERTY FOLDER glslang)
 # MachineIndependent
 ################################################################################
 set(MACHINEINDEPENDENT_SOURCES
-    MachineIndependent/glslang.m4
     MachineIndependent/glslang.y
     MachineIndependent/glslang_tab.cpp
     MachineIndependent/attribute.cpp

glslang/MachineIndependent/glslang.y

@@ -37,14 +37,6 @@
 // POSSIBILITY OF SUCH DAMAGE.
 //
 
-//
-// Do not edit the .y file, only edit the .m4 file.
-// The .y bison file is not a source file, it is a derivative of the .m4 file.
-// The m4 file needs to be processed by m4 to generate the .y bison file.
-//
-//    m4 -P
-//
-
 /**
  * This is bison grammar and productions for parsing all versions of the
  * GLSL shading languages.

glslang/updateGrammar

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/bin/sh
 
 # Copyright (C) 2020 The Khronos Group Inc.
 #
@@ -33,5 +33,4 @@
 # ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 # POSSIBILITY OF SUCH DAMAGE.
 
-m4 -P MachineIndependent/glslang.m4 > MachineIndependent/glslang.y
 bison --defines=MachineIndependent/glslang_tab.cpp.h -t MachineIndependent/glslang.y -o MachineIndependent/glslang_tab.cpp