i386-gen: preserve fp control word in gen_cvt_ftoi

- Use runtime function for conversion
- Also initialize fp with tcc -run on windows

This fixes a bug where
  double x = 1.0;
  double y = 1.0000000000000001;
  double z = x < y ? 0 : sqrt (x*x - y*y);
caused a bad sqrt because rounding precision for the x < y comparison
was different to the one used within the sqrt function.

This also fixes a bug where
  printf("%d, %d", (int)pow(10, 2), (int)pow(10, 2));
would print
  100, 99

Unrelated:
  win32: document relative include & lib lookup
  win32: normalize_slashes: do not mirror silly gcc behavior
  This reverts part of commit 8a81f9e103
  winapi: add missing WINAPI decl. for some functions

tcctok.h

@@ -194,8 +194,8 @@
      DEF(TOK__remu, "_remu")
 #endif
 #ifdef TCC_TARGET_I386
-     DEF(TOK___tcc_int_fpu_control, "__tcc_int_fpu_control")
-     DEF(TOK___tcc_fpu_control, "__tcc_fpu_control")
+     DEF(TOK___tcc_fpinit, "__tcc_fpinit")
+     DEF(TOK___tcc_cvt_ftol, "__tcc_cvt_ftol")
 #endif
 #ifdef TCC_ARM_EABI
      DEF(TOK___ashrdi3, "__aeabi_lasr")