seed PRNGs from System source instead of time.

src/random.cr

@@ -40,19 +40,14 @@ require "random/pcg32"
 module Random
   DEFAULT = PCG32.new
 
-  # Returns a `UInt32` read from a counter value generated by the cycle counter
-  # register, or the current time on ARM processors.
-  def self.new_seed : UInt32
-    {% if flag?(:arm) || flag?(:aarch64) %}
-      Time.now.ticks.to_u32
-    {% else %}
-      Intrinsics.read_cycle_counter.to_u32
-    {% end %}
+  # Initializes an instance with the given *seed* and *sequence*.
+  def self.new(seed, sequence = 0_u64)
+    PCG32.new(seed.to_u64, sequence)
   end
 
-  # Initializes an instance with the given *seed*. (Default: `#new_seed`)
-  def self.new(seed = new_seed)
-    PCG32.new(seed)
+  # Initializes an instance seeded from a system source.
+  def self.new
+    PCG32.new
   end
 
   # Generates a random unsigned integer.

src/random/isaac.cr

@@ -18,7 +18,13 @@ class Random::ISAAC
     init_by_array(seeds)
   end
 
-  def new_seed(seeds = StaticArray(UInt32, 8).new { Random.new_seed })
+  private def self.random_seeds
+    (uninitialized StaticArray(UInt32, 8)).tap do |seeds|
+      System::Random.random_bytes(seeds.to_slice)
+    end
+  end
+
+  def new_seed(seeds = self.random_seeds)
     @aa = @bb = @cc = 0_u32
     init_by_array(seeds)
   end

src/random/pcg32.cr

@@ -37,14 +37,22 @@ class Random::PCG32
   @state : UInt64
   @inc : UInt64
 
-  def initialize(initstate = UInt64.new(Random.new_seed), initseq = 0_u64)
+  def initialize
+    initialize(Random::System.rand(UInt64::MIN..UInt64::MAX), Random::System.rand(UInt64::MIN..UInt64::MAX))
+  end
+
+  def initialize(initstate : UInt64, initseq = 0_u64)
     # initialize to zeros to prevent compiler complains
     @state = 0_u64
     @inc = 0_u64
     new_seed(initstate, initseq)
   end
 
-  def new_seed(initstate = UInt64.new(Random.new_seed), initseq = 0_u64)
+  def new_seed
+    initialize(Random::System.rand(UInt64::MIN..UInt64::MAX), Random::System.rand(UInt64::MIN..UInt64::MAX))
+  end
+
+  def new_seed(initstate : UInt64, initseq = 0_u64)
     @state = 0_u64
     @inc = (initseq << 1) | 1
     next_u