arm: Comment out unused labels in simple_idct_arm

When building for iOS in thumb mode, gas-preprocessor.pl doesn't
mark unused labels as thumb functions (as it does for other
local labels, where it can figure out that they are functions
due to being referenced in branch instructions). This leads to
linker warnings for some of those local labels, such as:

ld: warning: ARM function not 4-byte aligned: __a_evaluation from
libavcodec/libavcodec.a(simple_idct_arm.o)

Therefore, comment them out since they don't have any function.
They do still have a value in documenting key points in the
assembly source though.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/arm/simple_idct_arm.S

@@ -83,7 +83,7 @@ __row_loop:
         orrs r5, r5, r7          @ R5=R4 | R3 | R2 | R7
         beq __almost_empty_row
 
-__b_evaluation:
+@@ __b_evaluation:
         @@ at this point, R0=block (temp),  R1(free), R2=ROWr32[1], R3=ROWr32[2], R4=ROWr32[3],
         @@     R5=(temp), R6=ROWr16[0], R7=ROWr16[1], R8-R11 free,
         @@     R12=__const_ptr_, R14=&block[n]
@@ -159,7 +159,7 @@ __end_b_evaluation:
         @@     R5=b2, R6=ROWr16[0], R7=b3, R8 (free), R9 (free), R10 (free), R11 (free),
         @@     R12=__const_ptr_, R14=&block[n]
 
-__a_evaluation:
+@@ __a_evaluation:
         @@ a0 = (W4 * row[0]) + (1 << (ROW_SHIFT - 1));
         @@ a1 = a0 + W6 * row[2];
         @@ a2 = a0 - W6 * row[2];
@@ -295,7 +295,7 @@ __end_row_loop:
         add r14, r0, #14        @ R14=&block[7], better start from the last col, and decrease the value until col=0, i.e. R14=block.
 __col_loop:
 
-__b_evaluation2:
+@@ __b_evaluation2:
         @@ at this point, R0=block (temp),  R1-R11 (free)
         @@     R12=__const_ptr_, R14=&block[n]
         @@ proceed with b0-b3 first, followed by a0-a3
@@ -357,12 +357,12 @@ __b_evaluation2:
         it    ne
         mlane r1, r10, r4, r1    @ R1-=W5*ROWr16[7x8]=b1
         @@ R4 is free now
-__end_b_evaluation2:
+@@ __end_b_evaluation2:
         @@ at this point, R0=b0,  R1=b1, R2 (free), R3 (free), R4 (free),
         @@     R5=b2, R6 (free), R7=b3, R8 (free), R9 (free), R10 (free), R11 (free),
         @@     R12=__const_ptr_, R14=&block[n]
 
-__a_evaluation2:
+@@ __a_evaluation2:
         @@ a0 = (W4 * col[8x0]) + (1 << (COL_SHIFT - 1));
         @@ a1 = a0 + W6 * row[2];
         @@ a2 = a0 - W6 * row[2];
@@ -414,7 +414,7 @@ __a_evaluation2:
         itt   ne
         subne r2, r2, r10        @ R2-=W2*ROWr16[6] (a1)
         addne r3, r3, r10        @ R3+=W2*ROWr16[6] (a2)
-__end_a_evaluation2:
+@@ __end_a_evaluation2:
         @@ at this point, R0=b0,  R1=b1, R2=a1, R3=a2, R4=a3,
         @@     R5=b2, R6=a0, R7=b3, R8 (free), R9 (free), R10 (free), R11 (free),
         @@     R12=__const_ptr_, R14=&block[n]
@@ -452,7 +452,7 @@ __end_a_evaluation2:
         strh r8, [r14, #96]
         strh r9, [r14, #112]
 
-__end_col_loop:
+@@ __end_col_loop:
         @@ at this point, R0-R11 (free)
         @@     R12=__const_ptr_, R14=&block[n]
         ldr r0, [sp, #0]         @ R0=block
@@ -463,7 +463,7 @@ __end_col_loop:
 
 
 
-__end_simple_idct_arm:
+@@ __end_simple_idct_arm:
         @@ restore registers to previous status!
         add sp, sp, #8 @@ the local variables!
         ldmfd sp!, {r4-r11, r15} @@ update PC with LR content.