Do not force inlining of indirect functions

* A function called indirectly cannot be decorated
  with `__attribute((always_inline))`, as this is
  guaranteed to only work with direct calls:
    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63220#c1

Bug: https://bugs.gentoo.org/798045

libFDK/include/fft.h

@@ -139,7 +139,7 @@ void ifft(int length, FIXP_DBL *pInput, INT *scalefactor);
  * bit scale headroom. The values are interleaved, real/imag pairs.
  */
 LNK_SECTION_CODE_L1
-static FDK_FORCEINLINE void fft_4(FIXP_DBL *x) {
+static inline void fft_4(FIXP_DBL *x) {
   FIXP_DBL a00, a10, a20, a30, tmp0, tmp1;
 
   a00 = (x[0] + x[4]) >> 1; /* Re A + Re B */
@@ -168,7 +168,7 @@ static FDK_FORCEINLINE void fft_4(FIXP_DBL *x) {
 
 #ifndef FUNCTION_fft_8
 LNK_SECTION_CODE_L1
-static FDK_FORCEINLINE void fft_8(FIXP_DBL *x) {
+static inline void fft_8(FIXP_DBL *x) {
   FIXP_SPK w_PiFOURTH = {{FIXP_SGL(0x5A82), FIXP_SGL(0x5A82)}};
 
   FIXP_DBL a00, a10, a20, a30;

libFDK/src/fft.cpp

@@ -170,7 +170,7 @@ [email protected]
 
 /* Performs the FFT of length 2. Input vector unscaled, output vector scaled
  * with factor 0.5 */
-static FDK_FORCEINLINE void fft2(FIXP_DBL *RESTRICT pDat) {
+static inline void fft2(FIXP_DBL *RESTRICT pDat) {
   FIXP_DBL r1, i1;
   FIXP_DBL r2, i2;
 
@@ -196,7 +196,7 @@ static FDK_FORCEINLINE void fft2(FIXP_DBL *RESTRICT pDat) {
 
 #ifndef FUNCTION_fft3
 /* Performs the FFT of length 3 according to the algorithm after winograd. */
-static FDK_FORCEINLINE void fft3(FIXP_DBL *RESTRICT pDat) {
+static inline void fft3(FIXP_DBL *RESTRICT pDat) {
   FIXP_DBL r1, r2;
   FIXP_DBL s1, s2;
   FIXP_DBL pD;
@@ -233,7 +233,7 @@ static FDK_FORCEINLINE void fft3(FIXP_DBL *RESTRICT pDat) {
 
 /* performs the FFT of length 5 according to the algorithm after winograd */
 /* This version works with a prescale of 2 instead of 3 */
-static FDK_FORCEINLINE void fft5(FIXP_DBL *RESTRICT pDat) {
+static inline void fft5(FIXP_DBL *RESTRICT pDat) {
   FIXP_DBL r1, r2, r3, r4;
   FIXP_DBL s1, s2, s3, s4;
   FIXP_DBL t;