Fortran (GFortran) -cpp, 304 bytes

#define w' on the wall'
#define p trim(x),trim(b)
character(16)a,b,x;a=' bottles of beer';b=a
do 5 i=99,1,-1;write(x,'(i0)')i;if(i<2)b=' bottle of beer'
if(i<99)print*,'Take one down, pass it around, ',p,w,'.',new_line(x)
5 print*,p,w,', ',p,'.'
print*,'Go to the store and buy some more, 99',a,w,'.';end

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The -cpp option allows me to #define macros.

Fortran (GFortran) -cpp, _409.. 266 bytes

#define w' on the wall'
#define p i,' bottle',char(n),' of beer'
#define q print"(*(g0))"
n=115;do5 i=99,1,-1;if(i<2)n=0
if(i<99)q,'Take one down, pass it around, ',p,w,'.',new_line(w)
5 q,p,w,', ',p,'.'
n=115;i=99;q,'Go to the store and buy some more, ',p,w,'.';end

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• -cpp allows me to #define macros
• macro p uses ASCII conversion, so a character variable 's' isn't needed
• macro q formats integers nicely, so a conversion of i to string isn't needed
• loop do5 (ungolfed do 5) loops around to label 5 two lines below

Fortran (GFortran) -cpp, 306 bytes

#define w' on the wall'
#define p trim(x),trim(b)
character(16)a,b,x
a=' bottles of beer';b=a
do i=99,1,-1
write(x,'(i0)')i
if(i<2)b=' bottle of beer'
if(i<99)print*,'Take one down, pass it around, ',p,w,'.',new_line(x)
print*,p,w,', ',p,'.'
enddo
print*,'Go to the store and buy some more, 99',a,w,'.'
end

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The -cpp option allows me to #define macros.

Fortran (GFortran) -cpp, 304 bytes

#define w' on the wall'
#define p trim(x),trim(b)
character(16)a,b,x;a=' bottles of beer';b=a
do 5 i=99,1,-1;write(x,'(i0)')i;if(i<2)b=' bottle of beer'
if(i<99)print*,'Take one down, pass it around, ',p,w,'.',new_line(x)
5 print*,p,w,', ',p,'.'
print*,'Go to the store and buy some more, 99',a,w,'.';end

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The -cpp option allows me to #define macros.

Fortran (GFortran) -cpp, 409... 312 bytes

#define w' on the wall'
#define p trim(x),trim(b)
character(16)a,b,c,x
a=' bottles of beer';b=a;c=' bottle of beer'
do i=99,1,-1
write(x,'(i0)')i
if(i<2)b=c
if(i<99)print*,'Take one down, pass it around, ',p,w,'.',new_line(x)
print*,p,w,', ',p,'.'
enddo
print*,'Go to the store and buy some more, 99',a,w,'.'
end

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The -cpp option allows me to #define macros. Maybe one day Fortran will have stretchy strings but for now I have to use trim() everywhere.

Fortran (GFortran) -cpp, 306 bytes

#define w' on the wall'
#define p trim(x),trim(b)
character(16)a,b,x
a=' bottles of beer';b=a
do i=99,1,-1
write(x,'(i0)')i
if(i<2)b=' bottle of beer'
if(i<99)print*,'Take one down, pass it around, ',p,w,'.',new_line(x)
print*,p,w,', ',p,'.'
enddo
print*,'Go to the store and buy some more, 99',a,w,'.'
end

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The -cpp option allows me to #define macros.