First-level of support for new aarch64 machines

Testing on Neoverse N1 (Ampere 3GHz). Tested only on a subset of phy-simulators.

- Changes:
- use SIMDE consistently
- adaptations of LDPC decoder generator for ARMv8 performance
- SIMDe modifications of Intel CRC to allow for aarch64 build.
  optimizations for 128-bit to improve performance of LDPC encode/decode
  on aarch64 (Neoverse 1)
- added BG2 files for 128-bit ldpc encoder (aarch64)
- testing on Xeon
- testing on x86
- minor changes to build/run on x86
- change in crc.h after returning to aarch64
- removed some warning in ldpc decoder generator for x86_64
- char
- Delete irrelevant constants
- Correctly declare variables
- Define stdbool for all architectures
- Remove definition of _MM_SHUFFLE and use SIMDE_MM_SHUFFLE
- Remove commented code
- Fix CMakeLists.txt
- Include SIMDE avx2 functions in tools_defs.h

radio/rfsimulator/stored_node.c

@@ -48,10 +48,10 @@ int fullread(int fd, void *_buf, int count) {
 int32_t signal_energy(int32_t *input,uint32_t length) {
   int32_t i;
   int32_t temp,temp2;
-  register __m64 mm0,mm1,mm2,mm3;
-  __m64 *in = (__m64 *)input;
-  mm0 = _mm_setzero_si64();//pxor(mm0,mm0);
-  mm3 = _mm_setzero_si64();//pxor(mm3,mm3);
+  register simde__m64 mm0, mm1, mm2, mm3;
+  simde__m64 *in = (simde__m64 *)input;
+  mm0 = simde_mm_setzero_si64(); // pxor(mm0,mm0);
+  mm3 = simde_mm_setzero_si64(); // pxor(mm3,mm3);
 
   for (i=0; i<length>>1; i++) {
     mm1 = in[i];
@@ -77,8 +77,6 @@ int32_t signal_energy(int32_t *input,uint32_t length) {
   temp2/=(length*length);
   //  temp2<<=(2*shift_DC);
   temp -= temp2;
-  _mm_empty();
-  _m_empty();
   return((temp>0)?temp:1);
 }