rebuild is 4x+ slower caused by non buffered file reading

[laizy]

$ time forge build                                                 
success.

real    0m1.274s
user    0m0.173s
sys     0m0.029s

$ time forge build
no files changed, compilation skippped.

real    0m5.053s
user    0m0.355s
sys     0m0.511s

 938 read(5, "{", 1)                         = 1
  939 read(5, "\n", 1)                        = 1
  940 read(5, " ", 1)                         = 1
  941 read(5, " ", 1)                         = 1
  942 read(5, "\"", 1)                        = 1
  943 read(5, "a", 1)                         = 1
  944 read(5, "b", 1)                         = 1
  945 read(5, "i", 1)                         = 1
  946 read(5, "\"", 1)                        = 1
  947 read(5, ":", 1)                         = 1

[mattsse]

vote close since will be resolved after bumping ethers @gakonst