fix invalid instruction mnemonics in powerpc fenv asm

there is no non-dot version of the andis instruction, but there's no
harm in updating the flags anyway, so just use the dot version.

src/fenv/powerpc/fenv.s

@@ -1,7 +1,7 @@
 .global feclearexcept
 .type feclearexcept,@function
 feclearexcept:
-	andis 3,3,0x3e00
+	andis. 3,3,0x3e00
 	# if (r3 & FE_INVALID) r3 |= all_invalid_flags
 	andis. 0,3,0x2000
 	stwu 1,-16(1)
@@ -29,7 +29,7 @@ feclearexcept:
 .global feraiseexcept
 .type feraiseexcept,@function
 feraiseexcept:
-	andis 3,3,0x3e00
+	andis. 3,3,0x3e00
 	# if (r3 & FE_INVALID) r3 |= software_invalid_flag
 	andis. 0,3,0x2000
 	stwu 1,-16(1)
@@ -53,7 +53,7 @@ feraiseexcept:
 .global fetestexcept
 .type fetestexcept,@function
 fetestexcept:
-	andis 3,3,0x3e00
+	andis. 3,3,0x3e00
 	# return r3 & fpscr
 	stwu 1,-16(1)
 	mffs 0