Implement some missing maths-related intrinsics

Author: tomaka

src/library.js

@@ -1398,10 +1398,16 @@ LibraryManager.library = {
   llvm_sqrt_f64: 'Math_sqrt',
   llvm_pow_f32: 'Math_pow',
   llvm_pow_f64: 'Math_pow',
+  llvm_powi_f32: 'Math_pow',
+  llvm_powi_f64: 'Math_pow',
   llvm_log_f32: 'Math_log',
   llvm_log_f64: 'Math_log',
   llvm_exp_f32: 'Math_exp',
   llvm_exp_f64: 'Math_exp',
+  llvm_trunc_f32: 'Math_trunc',
+  llvm_trunc_f64: 'Math_trunc',
+  llvm_floor_f32: 'Math_floor',
+  llvm_floor_f64: 'Math_floor',
 
   round__asm: true,
   round__sig: 'dd',

src/preamble.js

@@ -1746,6 +1746,11 @@ if (!Math['clz32']) Math['clz32'] = function(x) {
 };
 Math.clz32 = Math['clz32']
 
+if (!Math['trunc']) Math['trunc'] = function(x) {
+  return x < 0 ? Math.ceil(x) : Math.floor(x);
+};
+Math.trunc = Math['trunc'];
+
 var Math_abs = Math.abs;
 var Math_cos = Math.cos;
 var Math_sin = Math.sin;
@@ -1764,6 +1769,7 @@ var Math_imul = Math.imul;
 var Math_fround = Math.fround;
 var Math_min = Math.min;
 var Math_clz32 = Math.clz32;
+var Math_trunc = Math.trunc;
 
 // A counter of dependencies for calling run(). If we need to
 // do asynchronous work before running, increment this and